Obama says his 'red line' in Syria conflict is WMD

The U.S. so far has limited its aid to the Syrian rebels to humanitarian relief and communications equipment while trying to help the opposition come up with a blueprint for a post-Assad future, which the U.S. says is only a question of time. The approach aims to avoid a repeat of the post-Saddam chaos in Iraq by preventing sectarian strife and ensuring that the state continues to supply water, electricity and other basic services. Officials have called this regime change with a "soft landing."

Obama reiterated his call for Assad to step down, while offering a realistic assessment of the chances for a peaceful solution.

"So far he hasn't gotten the message, and instead has doubled down in violence on his own people," the president said. "The international community has sent a clear message that rather than drag his country into civil war, he should move in the direction of a political transition. But at this point, the likelihood of a soft landing seems pretty distant."