Ukraine has asked for military assistance from the U.S., a request that was believed to include lethal aid such as weapons and ammunition. Obama administration officials have said they were not actively considering lethal assistance for fear it could escalate an already tense situation.
The U.S. has already sent Ukraine other assistance, such as pre-packaged meals for its military.
In Brussels, NATO chief Anders Fogh Rasmussen said the military alliance would increase its presence in Eastern Europe, including flying more sorties over the Baltic region west of Ukraine and deploying allied warships to the Baltic Sea and the eastern Mediterranean. NATO's supreme commander in Europe, U.S. Air Force Gen. Philip Breedlove, told reporters that ground forces also could be involved at some point, but he gave no details.