President Putin has repeatedly said Ukraine plans to acquire nuclear weapons as a justification for Russia's invasion, although there's no evidence this is the case.
When it was part of the former Soviet Union, Ukraine did have nuclear weapons, but gave these up in the 1990s in return for security guarantees from the US, UK and Russia.
Last year, the Ukrainian ambassador to Germany, Andriy Melnyk, suggested if Ukraine couldn't join Nato, it might have to reconsider its nuclear-free status.
"Either we are part of an alliance such as Nato... or we have the only option - to arm by ourselves, and maybe think about nuclear status again."
However, the Ukrainian government has not expressed an intention to acquire nuclear weapons and a military strategy document published last year did not refer to them.