"There maybe some areas where there are tactical disagreements, " said Obama at a joint press conference with Merkelin the White House, referring to the possible shift from U.S. policy of not arming Ukrainian forces. "Not just Ukraine, but the principle of territorial integrity and sovereignty is one where we are completely unified."

　　"We are not looking for Russia to fail. We are not looking for Russia to be surrounded and contained and weakened," said Obama, although minutes ago he told reporters that unified Western acts to pressure the Kremlin would include continued efforts to bolster the presence of the North Atlantic Treaty Organization (NATO) in central and eastern Europe and continued isolation of Russia.

　　Obama says U.S.-EU unity reinforced on Ukraine crisis

　　Although he said whether Washington would send lethal weapons to Kiev was not yet decided, Obama left open the prospect, a scenario which opponents, including Merkel, feared would trigger a proxy war with Moscow.

　　"Now, it is true that if, diplomacy fails, what I've asked my team to do is to look at all options," he said. "And the possibility of lethal defensive weapons is one of those options that's being examined."

　　Meanwhile, Merkel reaffirmed that military solution, though still regarded as "low prospect" by Obama, would fail to solve the crisis. "We continue to pursue a diplomatic solution, although we have suffered a lot of setbacks," she said, hinting that a unilateral effort for Washington to arm the Ukrainian forces was not something Europe would like to see.

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

　　Merkel's visit to Washington was the latest in her shuttle diplomacy to solve the conflict in eastern Ukraine which has already claimed more than 5,300 lives. Just returning from a surprise visit to Moscow over the last weekend, Merkel would join her counterparts from France, Russia and Ukraine for a summit in Minsk on Wednesday.