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.
France, Germany, Russia and Ukraine are due to hold a new round of talks today in Minsk to try and find a political solution to the conflict in Ukraine.
More than 5,400 people have been killed in the fighting between Ukrainian forces and pro-Russia rebels since April 2014. The detailed proposals have not been released but the plan is thought to include a demilitarised zone of 50-70km (31-44 miles) around the current front line.
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.