Dozens of people have reportedly been arrested in the town of Madaya outside the Syrian capital, Damascus.
Residents said tanks rolled into the mountain town early on Thursday morning and that checkpoints had been set up at all entrances into the town."We are terrified here and don't understand why this is happening," an eyewitness told Al Jazeera. "There were no plans for protests today and neither had any protests been held in the city in the past two days."
Madaya has seen only limited anti-government rallies since the nationwide protests began last month.
The eyewitness said he saw tanks and armoured personnel carriers surrounding the town and closing off all exits at 4am. Mobile and landline communications and electricity were cut from 4am until 9am, he said.
An activist said five people had been killed when security services raided homes at dawn.
Activists are calling for big rallies to be held on Friday, dubbed 'Azadi Friday', using the Kurdish word for freedom as a gesture of national unity.