Calls grow to arm Ukraine, as European leaders scramble for last-ditch peace plan

European leaders scrambled Thursday to try and forge a diplomatic deal to end fighting in eastern Ukraine, in an apparent bid to head off U.S. consideration of lethal military aid for the Ukrainian government in its war against Russian-backed separatists.

At the same time, a bipartisan call in Congress for the U.S. to arm Ukraine was only growing, with lawmakers saying the military aid "is past due."

"We can't just stand by and let them be slaughtered by superior weapons," Sen. John McCain, R-Ariz., chairman of the Senate Armed Services Committee, said Thursday.

Top Obama officials are weighing pleas from both sides, without tipping their hand as to the next step as they hold a flurry of meetings with European counterparts.