A deadline for a U.N.-brokered cease-fire passed without reports of major violence at dawn Thursday, opposition activists said, just hours after Syria promised to observe a halt in fighting.

Under a peace plan by international envoy Kofi Annan, a truce was set for 6 a.m. Thursday, to be followed by negotiations between President Bashar Assad's regime and the Syrian opposition on a political transition.

But there were only dim hopes for an abrupt end to the bloodshed that has roiled Syria for 13 months and claimed more than 9,000 lives.

Syria has backtracked on previous peace plans, has characterized the uprising it's facing as a terrorist plot and has escalated shelling attacks on rebellious areas in recent weeks.

The regime also carved out an important truce condition when it announced Wednesday it would halt the fighting — saying it still has a right to defend itself against the terrorists that it says are behind the country's uprising.

Opposition activists said the Thursday morning deadline passed without reports of major violence.

The Britain-based Syrian Observatory of Human Rights, an activist group, said some shots were fired in the Damascus neighborhood of Qadam after midnight Wednesday and that an explosion went off in a car in a Damascus suburb, causing no injuries.

Fares Mohammed, an activist in the Damascus suburb of Zabadani, said an army tank at a checkpoint fired three shells at a nearby open area between 5:50 a.m and 6:10 am. Thursday.

The rebel Free Syrian Army, a fighting force determined to bring down Assad, has said it will abide by the cease-fire. But the opposition is not well organized, and there are growing fears of groups looking to exploit the chaos.

A cease-fire could pose a major risk for the Assad regime.

Many activists predict that huge numbers of protesters would flood the streets if Assad fully complies with the agreement and pulls his forces back to barracks. But Syria has ways to maintain authority even without the military, in the form of pro-regime gunmen called "shabiha" and the fiercely loyal and pervasive security apparatus.

Over the course of the uprising, the military crackdown succeeded in preventing protesters from recreating the fervor of Egypt's Tahrir Square, where hundreds of thousands of people camped out in a powerful show of dissent that drove longtime leader Hosni Mubarak from power.

On Wednesday, the White House cautioned that the Assad regime has reneged on promises to stop the violence in the past.

"What is important to remember is that we judge the Assad's regime by its actions and not by their promises, because their promises have proven so frequently in the past to be empty," White House spokesman Jay Carney told reporters in Washington.

Annan is scheduled to brief the U.N. Security Council on Thursday by videoconference from Geneva.