Reports of a planned "humanitarian intervention" in Ukraine by Russian armed forces have been met with "grave concern" by the Prime Minister and US President, Downing Street says.
Any such move would be "unjustified and illegal" and would prompt "further and tougher sanctions", the two leaders were said to have agreed in a telephone call.
"They reiterated that we continue to urge Russia to engage with the international community and the Ukrainian government to find a political solution to the crisis," a Number 10 readout of this afternoon's call said.
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A widespread frost across the UK as temperatures fall below freezing under clear skies.
After a vote tainted by reports of ballot-box stuffing and forced voting, Putin said Russia was ready to 'cooperate' with Britain.
Largely dry elsewhere tonight with a widespread frost and icy stretches