WASHINGTON - US President Barack Obama said on Tuesday that it is a "mistake" to think that the United States could take unilateral military action in Syria and that there is a simple solution to the crisis there.

"For us to take military action unilaterally as some have suggested, or to think that somehow there is some simple solution, I think is a mistake," the president said at a press conference at the White House.

Rejecting a parallel with Libya, where NATO's air raids helped the opposition topple Muammar Gaddafi and his government, Obama noted that for Libya the US and its allies mobilized the international community, won a UN Security Council mandate and had the "full cooperation" of the Arab states.

"And we knew that we could execute very effectively in a relatively short period of time," he added.

He described the situation in Syria as "a much more complicated " one, saying Washington will continue to work with key Arab states and its key international partners toward a resolution of the Syrian conflict.

"But the notion that the way to solve every one of these problems is to deploy our military, you know, that hasn't been true in the past and it won't be true now," he stressed.

Calling what is happening in Syria "heartbreaking and outrageous," he said it is not a question of whether Syrian President Bashar al-Assad leaves, "it's a question of when."