The US have this week accused Russia of a violation over the Minsk agreement on Ukraine, as the UN Security Council revealed a unanimous vote to approve the ceasefire deal.
Russian President Vladimir Putin
If Russia continues to violate the accord, Vice-President Joe Biden has promised that "the costs to Russia will rise".
Fighting continues with pro-Russian rebels saying they now control most areas surrounding the strategic town of Debaltseve.
Some media reports claim that Ukranian troops are now withdrawing from the town, shortly after Russian President Vladimir Putin urged the troops there to surrender. These reports have not yet been confirmed by the government, however.
International observers who have monitored the truce have been unable to enter the town - a key prize for rebels and goverment forces due to its positioning on a strategic railway line, linking rebel-held Donetsk and Luhansk.
Though a Russian-drafted resolution was approved by the Security Council, ambassadors exchanged angry words, with US Ambassador Samantha Power saying the agreement was welcome, but Russia had to prove its commitment to peace.
"Stop armind the separatists. Stop sending hundreds of heavy weapons across the border in addition to your troops. Stop pretending you are not doing what you are doing." she said.
She added: "Russia signs agreements then does everything within its power to undermine them. Russia champions the sovereignty of nations and then acts as if a neighbour's borders do not exist."
Her comments were deemed "offensive" by Russian Ambassador Vitaly Churkin.
He continued: "Since the very start of the crisis, Russia has actively called for a peaceful settlement through inclusive, transparent dialogue between all sides in the internal Ukrainian conflict."
After talks with Ukrainian President Petro Poroshenko, US Vice-President Joe Biden said that he "strongly condemned the violation of the ceasefire by separatist forces acting in concert with Russian forces, in and around the town of Debaltseve".
Biden added: "If Russia continues to violate the Minsk agreements... the costs to Russia will rise."
Mr Poroshenko went on to say that rebel attempts to take the town were a "cynical attack" on the agreed ceasefire.