"A resolution passed by the Rada, the Ukrainian parliament, on Nov. 18, 1993, attached conditions to its ratification of START that Russia and the United States deemed unacceptable. Those stated that Ukraine would only dismantle 36 percent of its delivery vehicles and 42 percent of its warheads; all others would remain under Ukrainian custody. Moreover, the resolution made those reductions contingent upon assurances from Russia and the United States to never use nuclear weapons against Ukraine (referred to as “security assurances”), along with foreign aid to pay for dismantlement.

In response, the Clinton and Yeltsin administrations intensified negotiations with Kyiv, eventually producing the Trilateral Statement, which was signed on Jan. 14, 1994. This agreement placated Ukrainian concerns by allowing Ukraine to cooperate in the transfer of the weapons to Russia, which would take place over a maximum period of seven years. The agreement further called for the transferred warheads to be dismantled and the highly enriched uranium they contained to be downblended into low-enriched uranium. Some of that material would then be transferred back to Ukraine for use as nuclear reactor fuel. Meanwhile, the United States would give Ukraine economic and technical aid to cover its dismantlement costs. Finally, the United States and Russia responded to Ukraine’s security concerns by agreeing to provide security assurances upon its NPT accession.

In turn, the Rada ratified START, implicitly endorsing the Trilateral Statement. However, it did not submit its instrument of accession to the NPT until Dec. 5, 1994, when Russia, the United Kingdom, France, and the United States provided security assurances to Ukraine. That decision by the Rada met the final condition for Russia’s ratification of START and therefore subsequently brought that treaty into force.

For more information, see Ukraine, Nuclear Weapons and Security Assurances at a Glance."

https://www.armscontrol.org/factsheets/lisbon-protocol-glance

:::