Syrian forces shot dead at least 20 civilians in attacks on pro-democracy demonstrations across the country on Friday, the Syrian human rights organisation Sawasiah said.

Syrians in their thousands took to the streets nationwide for the 17th consecutive Friday to demand an end to President Bashar Al-Assad's 11-year rule, activists said by telephone, defying an intensifying military crackdown on an uprising for political freedoms.

"The security forces are continuing violent repression against peaceful demonstrations demanding freedom and the downfall of the regime, firing live ammunition at most protests all over Syria on Friday," Sawasiah said in a statement sent to Reuters.

Sawasiah said it had the names of 20 people killed in the cities of Latakia, Hama, Homs, Deraa, Kiswa, Deir Al-Zor and in and around the capital Damascus.

Syrian authorities have expelled most independent journalists since the uprising began, making it difficult to verify reports of clashes, and do not usually comment on reports of killings.

Arrests continued across the country in the last two days, rights campaigners said, including hundreds of people in  Damascus, where they said Republican Guards deployed in force in the central Maidan district on Friday to prevent protests.

The official Syrian news agency said a member of the security police was killed in the town of Albu Kamal on the border with Iraq, and that saboteurs bombed an export oil pipeline near the central city of Homs on Friday.

The attack caused an oil leak, it said. Homs, where the army has deployed tanks, hosts one of Syria's two oil refineries and has been hit by big street protests.

"Our main goal is the downfall of the regime," a preacher told worshippers at the central Orontes Square in the city of Hama, scene of a massacre by the military in the 1980s.

Inspired by "Arab Spring" uprisings that toppled veteran leaders in Tunisia and Egypt, popular protests broke out in March against four decades of repressive rule by the Assad family.

 The unrest is now taking on sectarian overtones, with protesters from the Sunni Muslim majority pitted against minority Alawites who dominate the power elite.

Residents of Deir Al-Zor, speaking to Reuters by telephone,  reported fighting from the early hours of Friday, with tanks entering the city overnight.

The fighting later subsided but at least a dozen helicopters were seen ferrying troops to a military airport, and tank reinforcements arrived and took positions around the city, residents said.

There have been individual instances of Syrians using weapons during the unrest, for example defending their homes during assaults on restive cities by security forces.

But the fighting reported in Deir Al-Zor appeared to represent an armed response by a significant number of people to Assad's iron-fisted clampdown on public dissent. – Reuters