Previous truces have failed to take hold in Syria, which has been wracked by civil war since March 2011. In April, a cease-fire lasted barely a day before the killing resumed. In total, more than 32,000 Syrians have died since the conflict began, opposition activists say.

A spokesman for the Syrian National Council, an opposition coalition, said the truce is an attempt by President Bashar al-Assad to buy time.

"The whole world knows that the Syrian regime cannot be trusted and doesn't have any credibility in fulfilling any promise that they make to anyone," said George Sabra, a Paris-based spokesman for the Syrian National Council, which speaks for rebels fighting al-Assad. "The Assad regime is trying a diversion."

It's foolish to expect a total cease-fire, said Aram Nerguizian, a Middle East expert at the Center for Strategic and International Studies in Washington. A cease-fire in this context is about a larger goal of getting most rebel brigades and al-Assad forces to halt or reduce the killing.

The rebels themselves are partly to blame for the failure of this spring's cease-fire, Nerguizian said. They have been just as vicious in their killing as al-Assad's forces, he said.

But getting them to work together and resist the urge to fight, he said, is unrealistic.

Meanwhile, the United Nations' investigation into alleged war crimes in Syria is moving forward. The Geneva-based U.N. commission investigating war crimes announced Thursday it has requested a meeting with al-Assad to discuss gaining access to Syria for the team.

Carla del Ponte, who once served as prosecutor for the International Criminal Tribunal for the former Yugoslavia, is part of the commission. Noted for her investigation of war crimes in the Balkans in the 1990s, she cited similarities with past probes.

"The similarity is, of course, we are handling the same crimes, crimes against humanity and war crimes for sure," she said.

The Syrian government's isolation continued to grow.

In Jedda, Saudi authorities announced the deportation of three staff members of the Syrian Consulate General, the official Saudi Press Agency said Thursday. The move was taken because "authorities have concluded that their behaviors are incompatible with their consular duties and assignments," it said.