Annan said it was "time for countries of influence to raise the level of pressure on the parties on the ground." However, he had no specific proposals for changing his six-point peace plan, which he said Syria had not yet implemented but still might support in the future.

"The longer we wait, the darker Syria's future becomes," Annan said. "The humanitarian situation continues to deteriorate. ... We cannot just step back and do nothing."

Mood praised the work of his 300 U.N. monitors, whose mandate ends next month. He conceded, however, that they are now largely confined to bureaucratic tasks and calling Syrians by phone because of the insecurity and dangers on the ground.

"They are keen to resume their work. Their commitment to the Syrian people has not faltered," he said. "Whether more observers or arming observers would be relevant to the situation on the ground, I'm far from convinced that that would help the situation on the ground."