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.
Ukraine's President Petro Poroshenko says his country's key position at the Minsk peace talks later today is the need to secure an "unconditional ceasefire", Reuters reports.
He added that Ukraine is prepared to introduce martial law in all regions if the current crisis in the east of the country escalates.
The leaders of France, Germany, Russia and Ukraine are attending talks in Minsk to try to resolve the crisis.
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.