The northern Syrian town of Jisr al-Shughour is bracing for an assault by the military after the government said armed gangs had killed 120 security forces personnel.
Residents have posted messages on social networking site Facebook saying they fear a slaughter and appealing for help from outside world.
The government says it will act with force to restore control but activists say the source of the violence may be a military mutiny.
They reject the government's description of armed gangs, saying the uprising against the regime of President Bashar al-Assad is peaceful.
The BBC says communications have been cut around the town and details of the attack are impossible to verify.
Syria has banned foreign journalists reporting on events.
But state television said hundreds of gunmen had taken over Jisr al-Shughour, which lies about 20km from the Turkish border.
It said gangs using light weapons, grenades and stolen explosives earlier ambushed police as they approached the town.
The Sana news agency quoted an official as saying the gunmen were using residents as human shields.
