Positive Security Assurance

A positive security assurance (PSA) is a commitment by a nuclear-weapon state (NWS) to provide or support assistance to a non-nuclear-weapon state (NNWS) that becomes the victim of, or is threatened by, nuclear aggression. PSAs are typically offered to encourage states to join and remain in the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) by reducing the perceived security cost of forgoing nuclear weapons. They are distinguished from negative security assurances (NSAs), which are pledges not to use nuclear weapons against NNWS.

The principal multilateral PSA is contained in UN Security Council Resolution 255 (1968), adopted shortly before the NPT opened for signature. In it, the United States, the United Kingdom, and the Soviet Union declared that aggression with nuclear weapons, or the threat of such aggression, against a non-nuclear-weapon state would require immediate Security Council action, particularly by its nuclear-armed permanent members, to provide assistance to the victim. The resolution effectively links PSAs to the Council's enforcement machinery under Chapter VII of the UN Charter.

PSAs have notable limits:

• They depend on Security Council action, where any of the P5 can veto a response.
• They do not specify the form of assistance (military, diplomatic, technical, or humanitarian).
• France and China were not parties to Resolution 255, though both have since articulated their own assurance policies in varying terms.

PSAs reappear in debates around regional crises and treaty review cycles, including NPT Review Conferences, where NNWS — often through the Non-Aligned Movement and the New Agenda Coalition — press for stronger, legally binding assurances. The 1994 Budapest Memorandum, in which the US, UK, and Russia gave security assurances to Ukraine, Belarus, and Kazakhstan in connection with their accession to the NPT as NNWS, is frequently cited in this context, though analysts debate whether its commitments constitute PSAs, NSAs, or a weaker political undertaking. Russia's 2014 annexation of Crimea and its 2022 invasion of Ukraine intensified scrutiny of the credibility of such assurances.