|Critics say the Arab League mission has only provided diplomatic cover for Assad to pursue a crackdown [AFP]
Protesters have rallied against the government in huge numbers across many Syrian cities, in a day dubbed the "Friday for revolutionary detainees".
The demonstrations comes as Arab League peace monitors are set to meet with the bloc's foreign ministers in Cairo on Sunday to decide their future course of action after the culmination of their one-month mission in the country.
Syria said that the league’s mission could be extended if both sides agree to it but acknowledged that at this point it is not up to Damascus to decide this.
There were reports of scattered violence in areas following Friday's Muslim prayers.
Security forces prevented worshippers attending the Omari mosque in the southern town of Deraa, cradle of a 10-month-old revolt against President Bashar al-Assad, activists said.
The forces were out in full force as protests began in Aleppo, Latakia and Idlib, the British-based Syrian Observatory for Human Rights (SOHR) said.
A security officer, who had defected, was assassinated in Deraa, the SOHR said. Activists say at least twelve people were killed on Friday, including seven in Idlib.
Supporters of Assad also took out rallies in the capital Damascus.
Al Jazeera's Zeina Khodr, reporting from neighbouring Lebanon, said: "Today the protests were in solidarity for those who remain in prison."
Meanwhile, Ahmad el-Tayyeb, the grand imam of Cairo's Al-Azhar, the highest seat of Sunni Muslim learning, urged "Arab rulers to take the necessary measures to halt bloodshed in Syria", the state news agency MENA quoted him as saying on Friday.
Future of Arab mission
The widely criticised league mission hangs in the balance as General Mohammed Ahmed Mustafa al-Dabi, its head, prepares to report to Arab foreign ministers, who will decide on Sunday whether to extend it for a second month.
Two senior Arab League senior officials told the Associated Press news agency on Friday that the organisation was likely to extend its monitoring mission, initiated to verify whether an Arab peace plan was working.
The officials said that the direction within the Arab League was to keep the mission in place as the international community was not yet ready for "escalation" to an intervention in Syria.
NATO's most senior officer said on Thursday that the alliance was not planning or even "thinking" of intervening in Syria.
Critics say the Arab mission has only provided diplomatic cover for Assad to pursue a crackdown that has already killed more than 5,000 people by a UN count.
Burhan Ghaliun, the leader of the opposition Syrian National Council, also headed to Cairo to lobby the Arab ministers to refer the observer mission's findings to the UN Security Council for tough action.
Hundreds of people have been killed since the monitors arrived in Syria, where an armed revolt has grown in recent months, contesting Assad's grip on several parts of the country.
Some activists say as many as 740 civilians were killed in total during the last one month. One activist group, says security forces opened fire on protesters at least twenty times - sometimes while monitors were present.
That prompted one observer to quit, calling the mission "a farce".
'People losing faith'
New York-based Human Rights Watch said the league should publish the monitors' report in full and should urge the UN Security Council to impose targeted sanctions, including an arms embargo, to stop the killing in Syria.
"The Arab League should make its monitors' report public to address increasing concerns that its monitoring mission is being manipulated by the Syrian authorities," Sarah Leah Whitson, the group's Middle East director, said.
Al Jazeera's Khodr said: "Undoubtedly, the Arab League is divided and when you talk to any Syrian activist or protesters on the streets they will tell you the Arab League will not be able to come up with a united stance."
"So, most of people on the streets have lost faith in this mission, they don’t believe it [Arab mission] has been able to stop the violence. They don’t even understand its mandate," she said.
"That’s why there are growing calls for the Arab League to refer the file to UN Security Council."
The Security Council has appeared paralysed by divisions over Syria, with Russia and China opposing any tough action.
"They are hoping that if Arab League does that then it would put more pressure on Russia to stop blocking UNSC resolution because it would have the Arab cover," the Al Jazeera's correspondent said.
"Syrian government has stressed that they will not allow the mandate [Arab League] to change.
"Basically human rights groups are asking what they [Arab League] can do, what can they change on the ground."
Western sanctions on Syrian oil exports have cost the country $2bn since September, the state news agency SANA quoted Oil Minister Sufian Alao as saying.