Before her meeting with Annan, Clinton said they would look at "how to engender greater response by the government of Syria to the six-point plan that he has put forth."

Annan's plan calls for an end to violence followed by a political transition. Although Assad agreed to it, the violence has continued unabated with reports of brutal massacres against innocents.

Annan allowed that some people "say the plan is definitely dead." He asked rhetorically whether the problem is the plan or its implementation.

"If it's implementation, how do we get action on that? And if it's the plan, what other options do we have?" he said.

U.N. diplomats say Annan is proposing that world powers and key regional players, including Iran, come up with a new strategy to end the conflict.

In Damascus, government troops clashed with defectors from the Free Syrian Army in the Kfar Souseh district in some of the worst fighting yet in the capital. The clashes were a clear sign that the ragtag rebel group has succeeded in taking its fight into the regime's base of power.