Ukraine’s Russian-backed breakaway eastern territories have ordered military mobilisations amid a deadly escalation in fighting.
Men of fighting age in the self-declared people’s republics of Donetsk and Luhansk are being put on standby.
US President Joe Biden says he is convinced Russia will invade Ukraine, an allegation Moscow denies.
Western nations have accused Russia of trying to stage a fake crisis in the eastern regions as a pretext to invade.
International monitors report a “dramatic increase” in attacks along the line dividing rebel and government forces.
Two Ukrainian soldiers were killed and four injured by shelling on Saturday, the first deaths to be reported in weeks.
Mr Biden’s Defence Secretary, Lloyd Austin, said Russian forces were beginning to “uncoil and move closer” to the border with Ukraine.
In the German city of Munich, US Vice-President Kamala Harris told a security conference that if Russia did invade, the US and its allies would impose a “significant and unprecedented economic cost”, targeting its financial institutions and key industries, as well as those who aided and abetted such an invasion.
Echoing her remarks, UK Prime Minister Boris Johnson said that, in the event of an invasion, his country would “open up the Matryoshka dolls” of strategic Russian-owned companies and make it impossible for them to raise finance in London.
Mr Johnson had talks in Munich with Ukrainian President Volodymyr Zelensky, who was visiting for the security conference against the advice of President Biden, who had said it might not be a “wise choice” for the Ukrainian leader to be out of his country at this time.
The US estimates there are 169,000-190,000 Russian personnel massed along Ukraine’s borders, a figure that includes separatist fighters in Donetsk and Luhansk.
