Russian foreign minister Sergei Lavrov called on Ukraine to distance itself from what he called "extremists" in the east and pursue a course towards peace. He said "tangible progress" had been achieved in implementing measures agreed in Minsk this month and that the ceasefire was being "consolidated".
The US and Europe are not prepared to play games with Russia over the Ukraine crisis, John Kerry has said.
Speaking alongside Foreign Secretary Philip Hammond, the US Secretary of State said additional sanctions could be imposed on Russia over its "simply unacceptable" alleged role in supporting separatists in eastern Ukraine.
"Russia has engaged in an absolutely brazen and cyclical process over these last days," he told reporters in London.
"We are talking about additional sanctions, about additional efforts, and I'm confident over the next days people will make it clear that we are not going to play this game and be part of this kind of extraordinarily craven behaviour.
"This is behaviour that is completely counter to everything that the global community has worked to achieve since World War II."
Thousands of Russians are marching in Moscow to mark the first anniversary of what they viewed as a "coup" in neighbouring Ukraine.
14 soldiers died and many more were injured as Ukraine left the strategically important hub of Debaltseve.
Dramatic footage shows the moment a TV crew were forced to flee a huge explosion after a gas pipeline was hit by mortar fire in Ukraine.