Nineteen people have been reported killed as Syrian army forces spread through a restive mountainous area near the Turkish border.
The action by Syrian troops in the north-western area of Jabal al-Zawiya appeared to be aimed at preventing residents from fleeing to Turkey, where more than 10,000 Syrians have already taken shelter in refugee camps, activists say.
"They (the regime) fear there will be sympathy for the people who are fleeing, and they are frightened that this will cause international pressure to mount on the regime," said Mustafa Osso, a prominent Syrian-based human rights activist.
Only five Syrians made it across the border today, the lowest number in days, said Turkish officials.
Over the past week, more than 10,000 Syrians rushed across, fleeing their army's violent crackdown against demonstrators.
Syrian activists say more than 1,400 people have been killed as President Bashar Assad tries to crush three months of nationwide protests. The regime disputes that death toll and says "armed thugs" and foreign conspirators are behind the unrest.
Today Syrian forces were consolidating their hold on the Jabal al-Zawiya after two days of heavy shelling in the area, particularly in the village of Rameh, said Osso.
That assessment was repeated by Lebanon-based activist Omar Idibi and an eyewitness.
They said most people were killed on Wednesday and early today. Idibi said the death toll was likely to rise as people were pulled out of rubble from smashed homes in some areas.
Idibi said part of the fighting was prompted by Syrian forces trying to hunt down several dozen comrades who abandoned their arms. Some rebelled while in Rameh village, while others split away from the armed forces in earlier fighting this month in the nearby town of Jisr al-Shughour.
"They haven't been able to flee to Turkey," Idibi said. "They are fleeing from the advance of the Syrian army," he said. Idibi said eyewitnesses told him that Syrian forces were trying to seal gaps in the border with Turkey to prevent people from escaping.
Meanwhile, in the north-western city of Aleppo - some two-dozen miles from the army operations in Jabal al-Zawiya - several hundred demonstrators staged at least two anti-regime protests, according to Idibi.
A YouTube video uploaded by activists appeared to show several hundred men running down a street, filmed from a balcony several stories up. The men shout: "The people want an end to the regime!"
Another group of activists said the protesters were beaten up by pro-regime thugs.