There have been angry clashes between Russian and US envoys at the UN Security Council, after the US called a meeting to discuss Moscow’s troop build-up on its borders with Ukraine.
US Ambassador Linda Thomas-Greenfield said the mobilisation was the biggest Europe had seen in decades.
Her Russian counterpart accused the US of fomenting hysteria and unacceptable interference in Russia’s affairs.
The US and UK have promised further sanctions if Russia invades Ukraine.
UK Foreign Secretary Liz Truss said legislation was being prepared which would target a wider range than currently of individuals and businesses close to the Kremlin.
A US official said Washington’s sanctions meant individuals close to the Kremlin would be cut off from the international financial system.