Armed Syrian rebels captured dozens of members of the security forces by seizing two military checkpoints on Monday, the opposition said, even as the Arab League chief reported cautious progress in a peace monitoring mission.
The opposition said army deserters also clashed with security forces at a third checkpoint, killing and wounding an unspecified number of troops loyal to President Bashar al-Assad.
Assad is struggling to defeat a popular uprising and avoid becoming the latest president to be toppled by "Arab Spring" revolutions, after the leaders of Tunisia, Egypt, Libya and Yemen.
After nearly 10 months of violence in which the United Nations says more than 5,000 people have been killed, an Arab monitoring mission has spent the past week assessing Assad's compliance with a peace plan.
In partially upbeat comments, Arab League Secretary General Nabil Elaraby said Syria's military had withdrawn from residential areas and was on the outskirts of the country's cities, but gunfire continued and snipers were still a threat.
"The latest telephone report said there is gunfire from different places, which makes it hard to say who is shooting who," said Elaraby. "Gunfire should be stopped and there are snipers."
"We call upon the Syrian government to fully commit to what it promised," he said in Cairo.
The Arab League plan calls for Assad to withdraw troops and tanks from the streets, release detainees and talk to his opponents.
Elaraby said the monitors had achieved the release of 3,484 prisoners and succeeded in getting food supplies into Homs, one of the centers of the violence. "Give the monitoring mission the chance to prove its presence on the ground," he said.
But many Syrian opposition activists are skeptical that the mission can put real pressure on Assad to halt the violence.
The reported attacks on military checkpoints came three days after the anti-government Free Syrian Army said it had ordered its fighters to stop offensive operations pending a meeting with the Arab League delegates.
Rami Abdelrahman, director of the opposition Syrian Observatory for Human Rights, said Monday's operation took place in the northern province of Idlib. It was not immediately clear how many people had been killed or captured by the rebels.