"The possibility of lethal defensive weapons is one of those options that is being examined, but I have not made a decision about that yet," he said, speaking at a joint news conference with German Chancellor Angela Merkel at the White House.

Obama said U.S. consideration of supplying defensive weapons to Ukraine "is not based on the idea that Ukraine could defeat a Russian army that was determined. It is rather to see whether or not there are additional things we can do to help Ukraine bolster its defenses in the face of separatist aggression."

Separately, Merkel said that while there have been setbacks on reaching a diplomatic solution with Russia over Ukraine, such efforts will continue. She does not see a military solution to the crisis, she added.

"If at a certain point in time one has to say that success is not possible, even if one puts every effort into it, then the United States and Europe have to sit together and try and explore further possibilities of what one can do," she said.