Syrian troops killed seven civilians on Wednesday when they stormed two villages in the northwest to quash dissent against the regime of President Bashar al-Assad, a rights activist said.

The latest military action came as hundreds of lawyers staged a sit-in in the second city of Aleppo calling for freedom and the release of prisoners and regime loyalists held a counter-protest, activists said.

The Aleppo sit-in came as calls mounted on the Internet for a massive rally to take place Thursday in the the northern city -- the country's economic centre.

Tanks rolled into Mar-Ayan and Ihsem in the northwestern province of Idleb "opening fire and killing at least seven people," an activist in the region of Jabal al-Zawiyah, home district of the two villages, told AFP in Nicosia by telephone.

"The men are fleeing the villages because they are afraid they will be arrested," the activist said.

Earlier the head of the Syrian Observatory for Human Rights told AFP soldiers were conducting searches in the villages.

"Tanks and troop carriers entered the villages of Mar-Ayan and Ihsem. They are currently at the outskirts of Al-Bara," a hamlet known for its Roman remains, said Rami Abdel Rahman.

"The soldiers are deployed in the villages and are conducting searches," the head of the London-based Observatory said by phone.

The Observatory says 1,342 civilians have been killed since mid-March in a crackdown by President Bashar al-Assad's regime on the reformist movement and that 342 security force personnel have also died.

On Tuesday, tanks rumbled into another Idleb village, Al-Rami, which is just off the the highway leading to Aleppo.

Meanwhile some 300 lawyers organised staged a sit-in at the Aleppo courthouse chanting slogans for liberty and the release of political prisoners, activists said.

At the same time other, pro-regime lawyers gathered in a different room in the courthouse to pledge their alliegance to the regime.

Pro-democracy activists on Facebook have called for a rally to take place Thursday in Aleppo, where anti-regime protests have been largely muted since the pro-democracy movement broke out in mid-March.

"Revolutionaries, come to Aleppo and Idleb provinces... and go to central Aleppo tomorrow, Thursday, to protest and to light the spark of the Revolution," said the message posted on the Internet.

Abdel Rahman said a leader of the opposition Socialist Union Party was arrested in Aleppo on Tuesday evening, while a prominent member of Kurdish opposition party was detained in Al-Hasakah in the northeast.

Elsewhere, on Tuesday night, between 50,000 and 60,000 protesters marched through the eastern town of Deir Ezzor, where demonstrations have become a daily event, calling for the fall of the regime.

Meanwhile, author and activist Munzer Khaddam, who on Monday presided over a public meeting of opposition figures in Damascus, was taken to task by pro-regime supporters, activists said.

More than 150 militias loyal to the regime gathered outside Khaddam's Latakia home on Tuesday night and chanted "insults and slogans against liberty and the Damascus meeting," said Abdel Rahman.

The chants at the counterprotest, which another activist also said had taken place, were aimed at opposition figures who vowed Monday to press ahead with a peaceful uprising at a meeting in Damascus.

"The Syrian Observatory for Human Rights is holding the authorities responsible for the stupidity committed by pro-regime militias against protesters," Abdel Rahman said.

The militias, he added, had previously "participated in the repression of protesters, and have tortured people. In May, they even arrested two students and a caregiver to Banias, whose fate is still unknown."

"The Syrian authorities should take weapons away from illegal armed groups," he said.

The Syrian regime blames the disorder on "armed terrorist gangs", without recognising the scale of the protest movement.