BEIRUT - Syria warned the American and French ambassadors Wednesday not to travel outside the capital without permission, two weeks after they angered the regime by visiting a city that has become the centre of the country's four-month-old uprising.

If the U.S. and French envoys disobey the order, Syria will ban all diplomats from leaving Damascus, Foreign Minister Walid al-Moallem said during a lecture at Damascus University.

"We did not evict the two ambassadors because we want the relations to develop in the future and in order for their governments to review their stances toward Syria," al-Moallem said.

"If these acts are repeated, we will impose a ban preventing (diplomats) from going more than 25 kilometres (15 miles) outside Damascus," he said.

In Washington, State Department spokeswoman Heide Bronke Fulton said the order reflected a government that has something to hide. She said the U.S. ambassador and other diplomats must be allowed to travel throughout Syria to document the crackdown.

The French Foreign Ministry declined to comment.

Syria has come under withering international criticism and sanctions for its crackdown, which activists say has killed some 1,600 people, most of them unarmed protesters.

The regime has banned nearly all foreign media and restricted media coverage, making it nearly impossible to independently verify events on the ground.

On July 7 and 8, U.S. Ambassador Robert Ford and French Ambassador Eric Chevallier travelled to Hama, about 125 miles (200 kilometres) north of the capital, in separate trips to express support for the Syrian people to demonstrate peacefully. The State Department said friendly Syrians welcomed Ford and lavished his car with flowers and olive branches.

Hama residents told The Associated Press that the visits helped prevent attacks by security forces.

But the regime seized on Ford's visit to insist that foreign conspirators are behind the unrest, not true reform-seekers. Relations between the U.S. and Syria are chronically strained over Assad's ties with Iran. Within hours of the visit being made public, regime supporters attacked the U.S. and French embassies in Damascus, smashing windows and painting graffiti.

Three French Embassy workers were injured.

Also Wednesday, Syrian security forces swept through restive neighbourhoods, detaining dozens of people -- including a key opposition figure, activists said.

Security forces targeted suburbs of Damascus and the central city of Homs, which has seen some of the most intense and sustained violence in recent days. Up to 50 people have been killed there since Saturday, according to activists and witnesses. The figure could not be verified.

George Sabra, who heads the outlawed National Democratic Party, was picked up from his home in the Damascus suburb of Qatana, said the Local Coordination Committees, which help organize and document the protests in Syria. It was the second time that Sabra has been arrested since the uprising began.

In Homs, a father and his four sons were among those pulled from their homes overnight, said an activist in the city. He asked that his name not be published for fear of reprisals.

He added that soldiers and armoured personnel carriers were patrolling the city, along with plainclothes security agents carrying automatic rifles.

Also Wednesday, authorities released prominent political activist Ali Abdullah of the Damascus Declaration opposition group, three days after he was taken from his home near Damascus, the Local Coordination Committees said.

Abdullah, who has spent years in jail in the past, was released due to bad health, the group said. The 61-year-old underwent heart surgery earlier this month.