Protesters called for the ouster and prosecution of President Bashar Assad, whose autocratic regime has been blamed for the deaths of more than 5,000 people since pro-reform protests erupted in March. At least 10 people were shot dead.

Huge demonstrations rocked northwestern Idlib province and Douma, a Damascus suburb where protesters clashed with security forces who fired "nail bombs" to disperse them, said the Syrian Observatory for Human Rights.

At least 24 protesters were hurt when security forces fired "nail bombs to disperse tens of thousands of demonstrators in Douma," the watchdog said, adding that the protesters "hurled stones" in retaliation.

The reported use of nail bombs could not be independently verified.

The anti-government Free Syrian Army has ordered its fighters to stop offensive operations pending a meeting with Arab League delegates monitoring Assad's compliance with the peace plan, the rebels' commander said.

Col. Riad Al-Asaad said his forces had so far been unable to talk to the monitors, in the first week of their month-long mission, and he was still trying to contact them urgently.

"I issued an order to stop all operations from the day the committee entered Syria last Friday. All operations against the regime are to be stopped except in a situation of self-defense," he said.

"We have tried to communicate with them and we requested a meeting with the team. So far there hasn't been any success. We haven't been given any of the (phone) numbers for the monitors, which we have requested. No one has contacted us either."

How widely Turkey-based Al-Asaad's order is heeded by anti-government gunmen inside Syria is in question. A video shot by rebel fighters this week showed the ambush of a convoy of army buses in which, activists said, four soldiers were killed.

The Arab monitoring teams have encountered a range of problems, from hostility when they turn up under army escort, to random gunfire and communications breakdowns.

The mission has so far failed to end Syria's nine-month orgy of violence in response to demands for Assad to step down, although it was never advertised as a peacekeeping operation.