The White House said President Barack Obama urged Russian President Vladimir Putin in a phone call to agree to a peace deal.
"If Russia continues its aggressive actions in Ukraine, including by sending troops, weapons, and financing to support the separatists, the costs for Russia will rise," the White House statement added.
The US army will provide training to Ukrainian troops battling Russian-backed separatists in the country's east beginning in March, according to US Army Europe commander Ben Hodges.
Commander Hodges also claimed Russian has "ten battalions' on the border of eastern Ukraine. He added that European leader are worried that if rebels succeed in seizing the key railway town of Debaltseve "they may shift their attention to Mariupol."
Speaking during a visit to a NATO base in north-west Poland, Commander Hodges said the planned US training mission will involve one battalion of American soldiers training three Ukrainian battalions.
"We will train them in security tasks, medical (tasks), how to operate in an environment where the Russians are jamming (communications) and how to protect (themselves) from Russian and rebel artillery," he said.
Video footage recorded from Kramatorsk, deep inside Ukrainian-government controlled territory, shows rockets landing on civilian areas.
Video footage appears to show the moment a shell strikes a community soup kitchen in eastern Ukraine.
A mother in eastern Ukraine buries her son - yet another casualty in a civil war that is killing civilians with appalling randomness.