Syria braced Friday for a "Day of Defiance" by opponents of President Bashar al-Assad as they press an uprising against his rule in the face of a deadly crackdown that has drawn an international outcry.

Assad's troops have deployed in force in the Mediterranean protest hub of Banias and Ar-Rastan, another hotbed, activists said, after pulling out of the flashpoint town of Daraa in the south following a 10-day lockdown.

Dozens of armoured vehicles, including tanks, and troop reinforcements were deployed near Banias, an activist told AFP on Thursday, contacted by telephone.

"It looks like they are preparing to attack the town, like they did in Daraa," he said.

Hundreds of troops withdrew from Daraa on Thursday, and the military said the operation carried on overnight into Friday.

"Throughout the night, they withdrew from Daraa and this is continuing today. The troops' departure is gradual," General Riad Haddad, the military's political department chief, told AFP.

The army had rolled into the town on April 25 to quell the demonstrations that began three days after the unprecedented protest movement was born in Damascus on March 15.

Haddad said 600 people were arrested in Daraa during the 10-day operation.

On Wednesday, an activist had said around 100 tanks and troop transports converged on Ar-Rastan, near the central city of Homs.

"Reinforcements continue to mass at the northern entrance to Ar-Rastan and, according to our estimates, there must be 100 tanks and troop transports on the highway between Homs and Hama," the activist said.

As on Fridays for the past seven weeks, activists have vowed to stage protests against the regime of President Assad across the nation after the main weekly Muslim prayers.

The Syrian Revolution 2011, a Facebook group that has been a driving force of the protests, called for the "Day of Defiance" demonstrations, saying "Liberty is close."

The protests broke out in Damascus on March 15, inspired by Arab world uprisings that have already toppled long-time autocrats in Tunisia and Egypt this year.

They were promptly put down in the Syrian capital but moved to other centres including Daraa, Banias, Homs, nearby Hama, Aleppo in the north, and the majority Kurdish northeastern city of Qamishli.

Human rights groups say the crackdown has killed more than 600 people, while 8,000 people have been jailed or gone missing.

Syria's embattled government called upon citizens to refrain from taking part in the protests, in a statement carried by the state news agency SANA on Friday.

"The interior ministry calls upon citizens... to contribute significantly to stability and security... by refraining from engaging in any rallies or demonstrations or sit-ins," said the statement.

It warned the laws of Syria would be enforced to ensure security for citizens and the country's stability.

In a concession that failed to quell the protest movement, Assad decreed an end to five decades of emergency rule on April 21, but his forces have continued to use deadly force and carry out arbitrary detentions.

In the wake of the troop pullout from Daraa on Thursday, residents stepped out of their houses for the first time, most of them mute with fear as reporters toured the town accompanied by security forces.

"We didn't dare venture outside. I saw a sniper on a roof and a bullet passed within inches of me. Thank God, my life was saved," Najah Abdallah, a young mother wearing a black headscarf and holding her son by the hand, told AFP.

Frightened by the presence of cameras and supervised reporters, one man timidly offered his view: "Hopefully, everything is normal."

Suddenly, another man closer to the protesters joined in: "How can you say nothing is happening? Lies. Me, I'm not afraid to speak out. They just came to massacre us.

They ransacked my house, stole my money."

Others, however, recounted the official version of events.

"It was terror. There were hooded men with guns. They set up roadblocks and were taking passers-by off the streets. It was like a state within a state but we've been set free," said Abu Mohammed, a shopkeeper.

In New York, the United Nations said it would send a mission to Daraa after getting the go-ahead from Syrian authorities for a humanitarian team to enter the town.

Meanwhile, US President Barack Obama's administration defended itself against charges in Congress it has been too soft with the Syrian government over its deadly crackdown.