Syrian troops are reported to have shot dead at least six anti-government protesters in the city of Hama.
Activists said clashes continued into a second day in the central city as residents burned tyres and erected barriers to prevent tanks entering.
At least 20 people were arrested on Monday as troops sought to reassert control over the central city.
Hama was the scene of a brutal 1982 suppression of an uprising against President Bashar al-Assad’s father.
There were reports that Tuesday’s attacks centred on two districts north of the Orontes River, which divides the city of some 800,000 people.
Residents said that the dead included two brothers, Baha and Khaled al-Nahar, Reuters news agency reports.
Reports cannot be independently verified as the Syrian authorities have banned most foreign media from the country.
“There is an open civil defiance in Hama,” Rami Abdul-Rahman, the London-based director of the Syrian Observatory for Human Rights, told the Associated Press news agency.