Elite Syrian forces have moved swiftly through the country's restive north, raining tank shells on rebellious towns, torching farmland and shooting protesters who tried to tear down a poster of President Bashar Assad, activists and refugees said.
At least 32 people were killed, activists said, and undaunted protests extended to every major city.
The leader of neighbouring Turkey, angered by violence that has sent more than 4,000 Syrians streaming across the border, accused the Assad regime of "savagery".
Backed by helicopters and tanks, the troops responsible for most of yesterday's violence were believed to be from an elite division commanded by Assad's younger brother, Maher.
The decision to mobilise his unit against the most serious threats to the 40-year Assad regime could be a sign of concern about the loyalty of regular conscripts.
Syrians who escaped from the town of Jisr al-Shughour into Turkey said the army came after police turned their guns on each other and soldiers refused orders to fire on protesters last week.
Syrian state television has said 120 officers and security personnel were killed by gunmen. A man who remained behind said the few residents left were hoping barricades of burning tires could hold off the reinforcements surrounding them.
Twenty-five miles to the south-east in the town of Maaret al-Numan, thousands of protesters overwhelmed security officers and torched the courthouse and police station, and the army responded with tank shells, a Syrian opposition figure said.
Syria's state-run television appeared to confirm at least part of the report, saying gunmen opened fire on police stations, causing casualties among security officials.
Syria's government has a history of violent retaliation against dissent, including a three-week bombing campaign against the city of Hama that crushed an uprising there in 1982. Jisr al-Shughour itself came under government shelling in 1980, with a reported 70 people killed.
Confirming information out of Syria is difficult. Communications are cut in areas where the uprising is strongest. Syrians who speak openly face retribution from the regime, and foreign journalists have been expelled.