U.S. warns of catastrophic consequences if Russia uses nuclear weapons in Ukraine

Members of an electoral commission wait for voters near a destroyed residential building on the third day of a referendum on the joining of the self-proclaimed Donetsk People's Republic (DPR) to Russia, in Mariupol, Ukraine September 25, 2022. REUTERS/Alexander Ermochenko

The United States warned on Sunday of "catastrophic consequences" if Moscow uses nuclear weapons in Ukraine, after Russia's foreign minister said regions holding widely criticised referendums would get full protection if annexed by Moscow.

Votes were staged for a third day in four eastern Ukrainian regions, aimed at annexing territory Russia has taken by force. The Russian parliament could move to formalise the annexation within days.