Fred Tanner Friends and weapons: the architecture of security guarantees for Ukraine »There are no security guarantees except friends and weapons.« 1 President Zelensky‘s sober assessment at the UN General Assembly in September 2025 reflects current per ceptions of the role and usefulness of security guarantees. Security commitments under the term»security guarantees« have become rather ambiguous in high-stakes international security policies. Security guarantees typically come in one of two forms: binding alliance commitments – most notably NATO membership – or formal pledges by militarily superior states to defend weaker nations, sometimes reinforced by robust peacekeeping or enforcement operations. Effective guarantees require both legal obligations and credible military backing, as demonstrated by NATO‘s Article 5 collective defence provision. Ukraine‘s cur rent situation, however, satisfies neither criterion. But security guarantees are still in demand. In the event of termination of the conflict between Russia and Ukraine, a key challenge would be how to ensure that the ceasefire is not exploited by either side to rearm for renewed acts of war. The prospects of a peaceful settlement in Ukraine are limited. Apart from the brief Istanbul talks in March–April 2022, there were only limited signs of progress until early 2025, when the Trump administration opened communica tion channels with Russia. Since the outset of Russia’s invasion, Ukraine has sought credible defence commitments, recognising that opposition within NATO would block its accession and, with that, the protection under Article 5. For such commitments to be meaningful and credible, they must demonstrate the guarantor’s military capability, willingness and alignment of interests. 2 From a Western perspective, security guarantees are intended to reassure Kyiv and deter Moscow, albeit without committing them to go to war for Ukraine. While protection could be formalised for a post-war setting, certain forms of support, such as military aid, training and security assistance, have already been and continue to be provided by Western countries since Russia‘s invasion in 2022. 1 President Zelensky, statement UNGA, 24.09.25. 2 Lawrence Freedman(2025): Can the West guarantee Ukraine’s security?, in: The New Statesman, 31 January. Friends and weapons: the architecture of security guarantees for Ukraine 1

The historical record shows that security guarantees are difficult to define and usually emerge within broader political negotiations rather than being formalised in ceasefire or peace agreements or even laid out before the end of hostilities. Past cases illustrate this, such as the US–South Korea Mutual Defense Treaty following the Korean Armistice Agreement, and the US Congress‘s reinforced support for Taiwan through the Taiwan Policy Act of 2022, which authorised multi-year military aid, and the Fiscal Year 2025 National Defense Authorization Act, which expanded security cooperation. 3 While these measures strengthen Taiwan‘s defence capabilities, they deliberately fall short of providing an explicit, treaty-based security guarantee. During the Istanbul talks in spring 2022, Russia proposed that the permanent members of the UN Security Council be recognised as guardians of Ukraine’s post-conflict security regime. However, this would have granted Russia the power to veto Ukraine’s future security arrangements. Ukraine‘s counterproposal was fundamentally different: Kyiv sought a legally binding multilateral defence pact involving a broader coalition of states that would commit to taking action in the event of renewed aggression. The Ukraine-proposed Istanbul Communiqué also aimed to enshrine these commitments in a Treaty on Security Guarantees for Ukraine , which would have required ratification by participating states. 4 Normative foundations In addition to expressions of solidarity, security cooperation and hard security contributions, security guarantees often rest on normative foundations. Western states’ normative commitments to Ukraine are rooted in international law and liberal democratic principles. The basis for the West‘s military aid to Ukraine is the right to self-defence under Article 51 of the UN Charter. Furthermore, the West affirms Ukraine‘s sovereign right to freely choose its security alliances— a core principle of the Helsinki Final Act(HFA)— which challenges Russia‘s assertion of a»droit de regard« in its neighbourhood. However, Russia would counterpose to this the»indivisibility of security« principle enshrined equally in the HFA. Beyond normative arguments, the G7 and the EU emphasi se political alignment, highlighting their shared democratic values. The EU consistently reaffirms Ukraine‘s sovereignty within its 1991 borders and unequivocally supports its fu ture EU membership. This portrays the conflict not only as a geopolitical struggle, but also as a defence of fundamental liberal democratic principles against authoritarian aggression. This provides a basis for political frameworks that can accommodate a variety of security pledges. Table 1: Gradation of security guarantees It shows the gradation of security commitments, from non-binding political expressions to legally and militarily enforced obligations. Terms such as assurances, commitments, guarantees and treaties indicate different levels of credibility and enforceability. Soft(political/non-binding) Lowest level of commitment, typically non-legally binding. → Expressions of support → Political commitments → Assurances(for example, Budapest Memorandum 1994) → Pledges → Declarations/joint statements Intermediate(structured agreements) More formalised agreements, but usually short of full mutual defence obligations. → Partnership agreements(strategic partnerships, compacts) → Framework agreements → Security cooperation(training, intelligence, arms supply) → Defense cooperation treaties(without full alliance obligations) → Robust peacekeeping with enforcement capacity Hard(legal, military, full guarantees, ratified) Most credible and enforceable commitments, involving legal obligations and military presence. → Legally binding bilateral treaties → Mutual defence pacts → Extended deterrence commitments(for example, nuclear umbrella) → Alliance obligations(for example, NATO Article 5, US–South Korea Treaty) → Stationing of troops/permanent bases(trip-wire forces) Institutional and bilateral security layers for Ukraine The West has significantly advanced Ukraine‘s security integration by means of NATO summits and a structured security framework, focusing on solidarity, political rapprochement and long-term security support, short of Article 5 guarantees. A major upgrade was achieved at the 2023 NATO Vilnius Summit, at which a»fast track« to membership was established in the form of the NATO–Ukraine Council , which enhances Kyiv‘s political standing. This tra3 Samuel Charap, Joe Haberman, Katherine Anna Trauger, Benjamin Sakarin, Scott Savitz(2025): Guidelines for Designing a Ceasefire in the Russia-Ukraine War(Rand). 4 Institute for the Study of War(2025): Fact Sheet: Istanbul Protocol Draft Agreement, 24 February. Friends and weapons: the architecture of security guarantees for Ukraine 2

jectory was further reinforced at the 2024 NATO Washing ton Summit, at which NATO assumed direct coordination of all military aid and training through the NATO Security Assistance and Training for Ukraine(NSATU) initiative, thereby institutionalising NATO support. After US President Donald Trump rejected Ukraine’s NATO accession, however, the country’s membership seems more improbable than ever, leaving it without the umbrella of Article 5. The G7 Joint Declaration of Support for Ukraine was launched alongside the Vilnius Summit and has since been joined by numerous other nations. It established a framework for comprehensive bilateral security pledges. The core objective is to establish a sustainable Ukrainian defence force that is interoperable with NATO . This commitment includes providing ongoing military assistance, such as air defence and combat air capabilities, strengthening Ukraine‘s domestic defence industrial base and deepening extensive training and intelligence cooperation. While politically NATO membership remains unachievable, such institutional steps enhance the value of security cooperation and strengthen Ukrainian defence capabilities in practice. The European Union‘s comprehensive support for Ukrai ne was significantly strengthened with the signing of the Joint Security Commitments in June 2024. 5 This landmark agreement established the EU‘s first ever consultation pledge, committing the bloc to consulting with Ukraine immediately in the event of renewed aggression. The commitments also outline long-term cooperation in key areas such as defence, resilience, reform and countering hybrid threats. The agreement helps to shape Ukraine’s integration into the European security architecture, covering not only economic and political aspects, but also defence and resilience. The cornerstone of EU financial aid is the€50 billion Ukra ine Facility, which runs from 2024 to 2027. This is further bolstered by ongoing efforts to mobilise revenues from frozen Russian assets. In terms of military support, the EU is providing€5 billion annually via the European Peace Facili ty(EPF), training Ukrainian soldiers through the EU Military Assistance Mission(EUMAM) and fostering closer cooperation between defence industries, including the establishment of an Innovation Office in Kyiv. 6 Bilateral security agreements have become the primary means of providing Ukraine with long-term structured agreements outside NATO‘s Article 5. Adopting a»coalition of the willing« approach, European partners and other committed nations have each concluded a 10-year accord with Kyiv. These agreements are designed to ensure sustained assistance, focusing on continuous military aid, training programmes, intelligence cooperation, defence industry partnerships and contributions to Ukraine‘s post-war reconstruction. Although the agreements are bilateral, they are coordinated under the G7 umbrella to avoid fragmenta tion and ensure coherence among partners. 7 President Zelenskyy views these collective efforts, which now involve more than 30 participating states, as the foun dation for building a» New Security Architecture for Ukra ine «. 8 Central to this vision is the Ukraine Compact, which was established in July 2024 to coordinate and accelerate international commitments, and to reinforce mechanisms such as the Ukraine Defence Contact Group. The Compact includes plans to strengthen the Ukrainian armed forces, launch joint weapons production and define clear financial defence commitments. The effective implementation of these guarantees would provide Ukraine with»friends and weapons«, as well as creating a sustainable structure and networks of security assurances. US bilateral security agreements with Ukraine have shifted significantly. The US stands out as a special case among Ukraine’s bilateral partners because of its military capabilities and its pivotal role in European security. Under President Biden, officials presented a 10-year agreement as a»bridge to NATO membership«, providing interim support until formal accession. 8 Resembling deals with European partners, the agreement stopped short of NATO‘s Article 5, offering no automatic military intervention, only consultations and continued support, primarily through arms supply. The agreement commits the US to providing NATO-standard weapons such as Patriots and F-16s, as well as trai ning, intelligence sharing, logistics, joint defence-industrial projects and cooperation on cyber defence, counter-propaganda and demining. Following President Trump‘s return to office, the 2024 ac cord was not annulled, but rather reshaped by new arrangements. Trump abandoned unconditional, long-term commitments, instead making US support conditional and transactional. The 10-year framework became aspirational rather than binding, with aid now dependent on economic and diplomatic concessions on the part of Ukraine. US backing now proceeds on Trump’s terms and is linked to the mineral resources deal and peace initiatives that serve the interests of the US administration. Henceforth, US weapons for Ukraine must be purchased by the Europeans. For Ukraine, US security guarantees, both during the conflict and in its aftermath, remain ambiguous. 7 For an example of a bilateral security agreement, see the full text of the Agreement on Security Co-operation between the United Kingdom and Ukraine in the annex to this paper. 8 President Zelensky, statement UNGA, 24.09.25. 9 White House – Fact Sheet: U.S.-Ukraine Bilateral Security Agreement, 13 June 2024. Friends and weapons: the architecture of security guarantees for Ukraine 3

Peacekeeping as a security guarantee In post-conflict settings, peacekeeping operations often function as de facto tools of international stabilisation. In theory, a robust mission in Ukraine could fulfil this function by deterring violations and reducing the risk of renewed aggression. In practice, such a mission would depend on Russian consent in the UN Security Council and the OSCE framework, which seems politically unattainable. However, if deemed acceptable by the parties – as was the case with the OSCE Special Monitoring Mission to Ukraine (SMM) – international forces can serve as third-party compliance monitoring and reporting agents, thereby raising the costs of ceasefire violations. Such a mission could also act as a tripwire in the event, for instance, of a massive ceasefire violation triggering non-consensus based deployment of a reassurance force in support of Ukraine. But credibility depends on adequate resources, strict impartiality and sustained commitment, as well as mandates robust enough to prevent manipulation. The Minsk Agreements (2014/2015) illustrate the risks of weak enforcement: their implementation was systematically undermined by both sides, which ultimately contributed to their failure. 10 For a UN peacekeeping mission to be deployed in Ukraine, both Moscow and Kyiv must agree. Russia would almost certainly use this lever and attempt to impose conditions via the Security Council, reserving its veto as the ultimate means of blocking the mission. This illustrates why peacekeeping alone cannot provide credible guarantees without enforceable commitments that extend beyond the UN framework. The 2017 debates on peacekeeping in the Donbas region epitomise this deadlock. Russia proposed a narrowly scoped mission involving lightly armed UN troops whose role would be limited to protecting OSCE monitors along the line of contact. By contrast, Ukraine advocated a comprehensive UN enforcement mission covering the separation lines, occupied areas and the international border, regarding this as indispensable to restoring sovereignty within the framework of the Minsk Agreements. 11 Beyond the political deadlock, the operational challenges are immense. The line of contact stretches over 1,300 kilo metres, vastly exceeding the scale of traditional peacekeeping. Without resolving these fundamental challenges, peacekeeping risks becoming a facade rather than a genuine safeguarding arrangement that would provide some protection of post-conflict Ukraine. Consequently, significant attention has shifted towards technological solutions. The OSCE SMM pioneered the deployment of drones, cameras, acoustic sensors and satellite imagery. This has demonstrated that remote monitoring tools can substantially extend operational oversight, minimise personnel exposure and enable comprehensive coverage of expansive and hazardous territories. These innovations highlight a key point: peacekeeping operations on Ukraine‘s scale require a combination of traditional principles and state-of-the-art monitoring and surveillance technologies, including artificial intelligence(AI), possibly with the support of private actors. Such integration would be essential to making any mission operationally feasible if political progress ultimately permits deployment. 12 A deterrence or reassurance force is a large, capable military deployment that can alter an adversary’s cost–benefit calculation of aggression. Unlike peacekeeping operations, it is large and well-integrated enough to make a renewed attack prohibitively costly. According to Freedman, a deterrent force would consist of a sizeable foreign contingent integrated with Ukrainian forces and would be credible because it shifted the local balance of power. 13 This option is highly demanding, requiring tens of thousands of troops, advanced air power and major logistical support. European proposals have suggested a multinational force of 40,000–50,000 troops, though sus taining it would need over 100,000 personnel. France and the United Kingdom have proposed deployments with air, sea and land components, but the political will is limited, with scepticism for example in Poland and Italy. Even under favourable conditions, Europe cannot mount large-scale operations without US enablers, such as airlift, ISR and logistics, and currently there is no appetite in Washington for the provision of such support. Meanwhile, Moscow has categorically rejected the postconflict presence of NATO state armed forces in Ukraine, warning that such deployments would be tantamount to escalation and suggesting that only a limited, symbolic peacekeeping mission would be tolerable. The ongoing debate about the scale and nature of NATO‘s military involvement in Ukraine is thus fairly theoretical, as any significant engagement would inevitably lead to direct military confrontation between Russia and Europe. Beyond classic peacekeeping an extended deterrent posture by Europe against Russia could provide Ukraine with a critical, albeit indirect deterrent assurance. However, while Europe is striving for greater strategic autonomy, its current deterrence posture remains heavily dependent on 10 Charap et al.(2025). See n 3 above. 11 International Crisis Group(2017): Can Peacekeepers Break the Deadlock in Ukraine? Europe Report, No. 246, 15 December. 12 OSCE(2021): A Peaceful Presence: The First Five Years of the OSCE Special Monitoring Mission to Ukraine, authors: Fred Tanner, Hilde Haug, Tjasa Vendramin, Michael Raith, Malgorzata Twardowska, and Aniek van Beijsterveldt, edited by Heather Cantin, Walter Kemp, Richard Murphy, and Nicholas J. Stewart. OSCE Conflict Prevention Centre. 13 Freedman(2025), p. 9. See n 2 above. Friends and weapons: the architecture of security guarantees for Ukraine 4

American weapon systems and enablers. This casts doubt on the credibility of a fully independent European deterrent. Furthermore, uncertainty exists regarding the extent to which French and British nuclear forces can achieve a coherent deterrent effect across the full escalatory ladder. Although European states have increased defence expenditures and accelerated rearmament, the long-term scope of US involvement remains unclear. Adding to this uncertainty, there is a propensity for disagreement among European allies to rise in direct proportion to the pressure exerted by Russia and the ambiguity emanating from the United States. Russia‘s demands for treaty obligations have been extensive, culminating in an»ultimatum« issued to the US and NATO in late 2021. This framework sought legally binding assurances to halt NATO expansion and limit the presence of Western military forces near Russia’s borders. The proposals included mutual undertakings not to use force, restrictions on military activities(including bans on foreign bases and nuclear weapons outside national territory) and prohibitions on using third-party territory for attacks. They also included provisions for consultations and peaceful dispute settlement. 14 Even after Russia‘s full-scale invasion of Ukraine in 2022 Moscow insists on immediate tactical requirements for any cessation of hostilities. Foreign Minister Lavrov has emphasised that mechanisms to identify ceasefire violations are essential to credible guarantees, arguing that Ukraine would otherwise exploit a ceasefire to rearm. 15 Overall, Russia’s enduring objectives are to impose military restrictions such as preventing NATO infrastructure from being located near its borders and prohibiting the presence of advanced Western weapons in Ukraine. They also include political demands such as ensuring Ukraine’s neutrality and recognising territorial changes. The strategic aim is clear: to limit Western military influence in Eastern Europe and establish a recognised»sphere of influence«. Both the original demands and the current operational requirements are likely to influence the outcome of future US–Russian negotiations and will shape the Russian position on any peacekeeping mission. Conclusions The debate on security guarantees for Ukraine underscores the need for a differentiated approach that calibrates policies and commitments. Formal assurances have repeatedly shown their fragility, whereas credible deterrence depends on both capability and political will. Historical precedents, particularly the Budapest Memorandum, and to a certain degree also the 2014/2015 Minsk Agreements highlight the dangers of relying on ambiguous promises without enforceable mechanisms. Ukraine is unlikely once again to entrust its survival to such arrangements and looks for alternatives, seeking more incremental but also more credible measures. In practice and in acknowledgment of past failures, Western partners have adopted a layered approach comprising bilateral security agreements, NATO integration short of Article 5, EU commitments and sustained military aid. Ho wever, these remain partial substitutes rather than definitive guarantees. Against this backdrop, the» steel porcupine « concept has emerged, focusing on domestic Ukrainian strength instead of relying on foreign assistance. 16 This concept envisages Ukraine as a heavily armed and fortified state, making any renewed Russian attack prohibitively costly. Ukraine is seeking to build resilience and self-sufficiency by prioritising advanced air defences, long-range strike systems, hardened infrastructure and integration into Euro-Atlantic training, intelligence and logistics networks. Ultimately, Ukraine‘s future security lies not in symbolic pledges and expressions of solidarity, but in a combination of allies and weaponry. This would entail deepening institutional ties to the EuroAtlantic community while developing a national defence posture capable of deterring aggression on its own territory. Such an approach accepts that security guarantees are far feebler than the term suggests and shifts towards a deterrence posture based on domestic strength plus a number of support structures. To use President Zelenskyi’s words, it tries to keep friends close and enough weapons ready. 14 Steven Pifer(2021): Russia’s draft agreement with NATO and the United States: Intended for rejection?, in: Commentary, Brookings, 21 December. 15 CBS(2025): Face the Nation interview with Foreign Minister Lavrov, 27 April. 16 Andriy Zagorodnyuk(2025): Ukraine’s New Theory of Victory Should be Strategic Neutralization, Carnegie Endowment for International Peace, 18 June. Friends and weapons: the architecture of security guarantees for Ukraine 5

Annex Agreement on Security Co-operation between the United Kingdom of Great Britain& Northern Ireland and Ukraine , signed on 12 January 2024, is the first bilateral security accord concluded following the G7 Joint Declaration of Support for Ukraine. This agreement is valid for ten years and is designed to provide Ukraine with long-term security support outside of NATO‘s Article 5. The summary of the key commitments and provisions is as follows: 1. Future Security and Deterrence → Consultation in case of attack : In the event of a future Russian armed attack, the Participants will consult within 24 hours to determine the necessary measures to counter and deter the aggression. → Sustained assistance : Both sides commit to providing swift and sustained security assistance , modern military equipment and economic assistance, acting in accordance with their respective legal requirements. However, the agreement does not contain a mutual defence clause equivalent to NATO‘s Article 5. → Long-term goal : The accord aims to support an independent, democratic and sovereign Ukraine capable of defending against future attacks and accelerating its transition to NATO interoperability. 2. Defence and Military Cooperation → Military aid : The UK commits to the continued provision of security assistance and modern military equipment, prioritising areas such as air defence, artillery, long-range firepower, and armoured vehicles . → Defence industrial base : A central focus is to develop Ukraine‘s defence industrial base and identify opportunities for closer defence industrial partnerships, including for the localisation and joint production of defence products. → Capability coalitions : The UK plays a significant role in capability coalitions, including jointly leading the Maritime Security Capability Coalition to enhance naval capabilities and security across the Black and Azov Seas. 3. Non-Military and Institutional Cooperation → Cyber and intelligence : The Participants will work together on intelligence and security co-operation to detect, deter and disrupt Russian conventional aggression and hybrid warfare. This includes strengthening Ukraine‘s cyber resilience through advice and industry support. → Reforms and reconstruction : The agreement reaffirms support for Ukraine‘s democratic and anti-corruption reforms and commits to providing assistance for post-war reconstruction and strengthening economic stability. 4. Timeframe and NATO → Duration : The agreement is valid for a period of ten years. → NATO path : The Participants intend that the agreement remain in force as Ukraine pursues its path to future membership of the Euro-Atlantic community. In the event that Ukraine becomes a member of NATO before the expiry of the agreement, the participants will decide on its future status. About the Author Fred Tanner is Member of the Advisory Board, FES Regional Office for International Cooperation in Vienna and Faculty Associate at CCDP, Geneva Graduate Institute. He is also Senior Adviser, at the Centre for Strategic Analysis(CSA), Vienna. Before that he served as Senior Advisor of the OSCE Secretary General and Director at the GCSP. The author acknowledges with gratitude the support and insights of Christos Katsioulis. General Information Publisher FES Regional Office for International Cooperation Cooperation and Peace Reichsratsstr. 13/5, A-1010 Vienna Phone:+43 1 890 38 11 205 Responsible Christos Katsioulis Commercial use of all media published by the Friedrich-EbertStiftung(FES) is not permitted without the written consent of the FES. The views expressed in this publication are not necessarily those of the Friedrich-Ebert-Stiftung or of the organisation for which the author works. The Friedrich-Ebert-Stiftung e.V. holds the rights to the photographic material. Use of the photographic material is only permitted when reporting on the Friedrich-Ebert-Stiftung e.V. Commercial use of the photographic material is not permitted. If you have any questions concerning the clarification of rights, please contact the FriedrichEbert-Stiftung e.V. October 2025 © Friedrich-Ebert-Stiftung e.V. ISBN 978-3-98628-790-0 FES Regional Office for International Cooperation Cooperation and Peace Friends and weapons: the architecture of security guarantees for Ukraine 6