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.
More top news
The final of the 'Big 6' energy firms to cut prices - EDF - has announced it is reducing gas tariffs by just 1.3%.
Memorial and Learning Centre to use digital technology to commemorate and educate about the Holocaust
ITV News returns to Bergen-Belsen with Bernard Levy, a Jewish British army officer who was only 19 years old when he liberated the camp.