The United States is exploring ways its military can help Ukraine defend itself in the event of an attack by Russia.
According to Western intelligence estimates, there are almost 100,000 Russian troops near Ukraine's borders as it is believed Moscow might be planning a large-scale military offensive in coming weeks.
Last week U.S. President Joe Biden pledged to make it "very, very difficult" for Russia's Vladimir Putin to take military action amid spiralling tensions with Ukraine.
"Ukraine reached out [to the United States] and basically said, look, you have this [commitment] under the Budapest Memorandum to provide us with defence capabilities, including nuclear deterrence," says a senior intelligence source who did not want to be identified.
"Deploying U.S. nuclear weapons in Ukraine as [deployed] on Turkish soil in 1959 to deter Soviet aggression is among the last-resort options being considered. This would make [invasion] "very, very difficult" for Russia as President Biden put it. However, this would not be a decision to take lightly."
When the Soviet Union collapsed in 1991, nuclear weapons were scattered across the former Soviet republics. Ukraine had inherited the third largest nuclear arsenal in the world, including some 1900 strategic nuclear weapons designed to strike the United States. Worried of the prospect of conflict among nuclear-armed states, the U.S. led international efforts to denuclearize Ukraine, Belarus and Kazakhstan.
Ukraine wanted international guarantees or assurances of its security and sovereignty once it got rid of the nuclear arms.
The Budapest Memorandum refers to a 1994 international agreement under which the United Kingdom and the United States, later joined by France and China undertook to provide security assurances to Ukraine.
In return, by mid-1996, Ukraine transferred the Soviet-made nuclear weapons to Russia and acceded to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) as non-nuclear-weapon states.
Russia annexed Crimea from Ukraine in 2014 and has since backed armed separatists fighting Kiev in the east of the country with more than 13,000 dead so far. Russia privately seeks binding guarantees from the U.S. precluding NATO’s expansion to Ukraine.
