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.
President Barack Obama's administration is reportedly considering providing Ukrainian forces with "defensive weapons and equipment".
Secretary of State John Kerry and US Joint Chiefs Chairman Martin Dempsey are said to be open to fresh discussions of the idea, the New York Times reported, citing unnamed officials.
The report also claimed Nato military commander General Philip Breedlove supported the move.
A spokesman for General Breedlove declined to comment on his view when asked by the newspaper.
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.