|Deir al-Zor has seen heightened crackdowns on protesters since its governor was replaced last week [Reuters]
Syrian security forces have fired at demonstrators in the southern city of Deraa as tens of thousands again took to the streets across the country after Friday prayers to demand the downfall of President Bashar al-Assad, witnesses and activists said.
"They are firing at demonstrators in alleyways and people are running for cover. Protesters have been trying to avoid heavy security in main streets," a resident of Deraa told the Reuters news agency.
Amer al-Sadeq, of the Syrian Revolution Co-ordinators Union, told Al Jazeera from north of Damascus that some protesters had been killed.
The report could not be independently verified as foreign media are not allowed in the country.
"So far we have received reports of at least eight people killed, including a child who has been clinically announced dead," he said.
"He is in the hospital in Latakia where three people were killed by live ammunition.
"Also, we have received reports that tanks were used in Deir al-Zor and helicopters are being sent there as we speak."
"The regime insists on confronting these protests with heavy power, with live ammunition, with security forces and with killing," Sadeq said.
Security forces also used tear gas to try to disperse demonstrators in Deraa, witnesses said. There were no immediate reports of injuries there, but witnesses reported casualties in other parts of the country.
Activists earlier said security forces killed at least six people during overnight raids in Deir al-Zor province and the suburbs of Damascus, the AFP news agency reported.
This came amid reports of defected troops clashing with soldiers loyal to the ruling Baathist party.
"Tanks entered the city overnight, but there is talk of entire army units defecting. Electricity and communications have been cut," a resident, who declined to be named, told Reuters.
On Sunday, Assad replaced the civilian governor of Deir al-Zor province with Samir Othman al-Sheikh, a secret police officer, two days after roughly 500,000 people held demonstrations against his government.
Last week the army surrounded the town of Albu Kamal on the easternmost edge of Deir al-Zor after 30 soldiers defected after the killing of protesters, residents said.
Meanwhile, earlier on Friday, a bomb blast struck a major oil pipeline in western Syria, causing oil to spill into a nearby lake. State television said the explosion was a "terrorist'' attack by a group of "saboteurs".
It was the second incident involving an oil pipeline in a month, and the second time this week that authorities accused saboteurs of striking installations.
Authorities said the pipeline carries crude from the oilfields in the oil-rich eastern Deir al-Zor to one of Syria's two oil refineries in the coastal town of Banias, the main point of export for Syrian oil. The second oil refinery is in the central city of Homs.
State TV said the blast hit near the western town of Talkalakh between Homs and Tartous, near the Tal Hosh dam, and left a 10-metre-deep crater. The TV said the "terrorist attack sought to cause oil to leak into
the dam's waters in order to damage agricultural crops in the area".
Sifian Allaw, the oil minister, said 1,500 barrels of crude oil leaked from the struck pipeline into the water behind the dam.
Syria's oil exports are among the main earners of foreign currency for the government, especially now that the uprising has hit the tourism industry.
Syrian authorities have unleashed a brutal crackdown in an effort to crush the revolt against Assad, and activists say more than 1,600 civilians have died since the protests erupted in mid-March.
The government blames the unrest on terrorists and foreign extremists, not true reform-seekers.
Syrians across the country continued their mass protests after Friday prayers in what has become a weekly ritual of demonstrations and retaliation by security forces.
Opposition groups have dubbed this Friday's protests 'Your silence is killing us', in an attempt to mobilise large sections of the population that have not yet joined the protests, as well as Arab leaders who have remained silent on the crackdown in Syria.
In the Damascus suburb of Qatana, security forces armed with machine guns and other weapons arrived in pickup trucks overnight and carried out the arrests before searching for more protesters.
The sweep came as people took to the streets to protest after security forces killed 11 people on Wednesday in Kanaker, 50km southwest of the capital, said human rights activists.