The Syrian National Council said military troops and vehicles had surrounded the western city and thousands of troops were manning more than 60 checkpoints just inside the city.

"Evidence received from reports, videos and information obtained by activists on the ground in Homs indicate that the regime is paving the way to commit a massacre in order to extinguish the revolution in Homs and to discipline, by example, other Syrian cities that have joined the revolution," the council said.

At least 17 people were killed in Homs and at least 29 were killed elsewhere across Syria on December 9, according to the Local Coordination Committees of Syria, an opposition group. It said women, children and dissident soldiers were among the dead.

The United Nations said last week that more than 4,000 people have died in Syria since a government crackdown against protesters erupted in mid-March.

The regime's actions have outraged world powers and sparked sanctions by the Arab League, Turkey, the US and the EU.