Syrian security forces killed at least eight civilians on Friday as more than 1.2 million protesters swarmed cities in the north and east to protest against President Bashar al-Assad's rule, activists said.

Activists had called for Friday's demonstrations on Facebook group The Syrian Revolution 2011, a driving force behind more than four months of anti-regime protests, to show support for the flashpoint city of Homs.

More than 50 people have been killed since Saturday in central Homs, activists have said, accusing the regime of sowing sectarian strife among the city's Christian and Muslim inhabitants.

More than 1.2 million Syrians swarmed the streets of the eastern oil hub of Deir Ezzor and Hama in the north, the head of the London-based Syrian Observatory for Human Rights, Rami Abdel Rahman, told AFP in Nicosia.

"More than 1.2 million people marched: in Deir Ezzor there were more than 550,000, and in Hama more than 650,000," Abdel Rahman said.

Security forces, braced for anti-regime protests, and pro-government agents used deadly violence to disperse demonstrators in several areas, including Homs and Aleppo, activists said.

"Two demonstrators were knifed to death outside the Amneh mosque in Aleppo by pro-regime militiamen who stormed the mosque and attacked worshippers," said activist Abdel Karim Rihawi.

Rihawi, who heads the Syrian League for the Defence of Human Rights, reported another death in the province of Aleppo and said dozens more were wounded or arrested throughout Syria's second city.

In Homs, "two protesters were shot dead by security forces who dispersed a demonstration in the neighbourhood of Al-Khaldiyeh," Rihawi added.

A protester was also killed by security forces in Kfar Ruma, in Idlib province on the border with Turkey, he added.

Two more were shot dead in the Mleiha region of greater Damascus "when security forces opened fire," according to Abdel Rahman, adding that several other people were wounded in the crackdown.

Security forces also wounded several people when they fired on demonstrators in Idlib, activists said.

In Hama, 210 kilometres (130 miles) north of Damascus, demonstrators chanted slogans "in favour of national unity and against sectarianism," while also calling "for the fall of the regime," Abdel Rahman said.

The authorities are trying to quell protests in the city where rights groups said 25 civilians were killed by the security forces last Friday. Hama has seen some of the largest recent protests against Assad's regime.

Memories in Hama remain strong of a 1982 crackdown by the president's father, Hafez al-Assad, against Islamists that left 20,000 people dead.

In Deir Ezzor near the border with Iraq, some 430 kilometres east of Damascus, "daily sit-ins are taking place calling for the fall of the regime," Abdel Rahman said.

Syrian television denied that more than one million people had mobilised against the regime, saying that only "about 2,000 people took part in Friday's demonstration in Deir Ezzor."

The reports could not be independently verified.

Thousands of protesters also marched in the capital Damascus, despite a clampdown by security forces ahead of Friday's weekly Muslim prayers.

Around 5,000 people thronged the neighbourhood of Midan and thousands more emerged from three mosques in Hajar al-Aswad chanting slogans calling for freedom, activists said.

Earlier Abdel Rahman told AFP that army and security forces had barricaded the district of Rukneddin, isolating the mostly Kurdish-populated neighbourhood, while a clampdown was also imposed on Qabun district.

"Rukneddin is completely isolated. Barricades have been erected at all the entrances. Thousands of security officers are patrolling and conducting searches of homes and making arrests," he said.

Since the start of anti-regime protests in Syria in mid-March, pro-democracy demonstrators have chosen Friday -- the weekly day of rest when devout Muslims gather for midday prayers -- to vent their rage and call for change.

Meanwhile France on Friday condemned the repression in Syria, particularly the crackdown on dissent in Homs, with the foreign ministry spokesman saying the army should protect the people rather than "sow terror."