Army deserters on Saturday took the town of Douma northeast of Damascus on Saturday after fierce fighting, activists said, a day before the Arab League decides the future of its Syria observer mission.
The League looks set to extend the mission at a ministerial meeting on Sunday, despite heavy criticism that it has failed to stem the violence, and fresh reports on Saturday of civilian deaths.
International pressure has been steadily growing on Damascus with, according to UN figures, more than 5,400 people killed in the 10 months since anti-government protests started last March.
There was no independent confirmation that Douma had been taken or of fighting there, as foreign reporters are generally not allowed access.
But the British-based Syrian Observatory for Human Rights, citing militants on the ground, said the mutineers had seized control of the entire town, around 20 kilometres (12 miles) from the capital.
"Groups of deserters took control of all districts in the town of Douma, near Damascus, after fierce fighting on Saturday with Syrian security forces," the Observatory's chief Rami Abdel Rahman told AFP.
He said there were reports of fighting continuing late Saturday.
Earlier, the Observatory said four civilians were killed in Douma when security forces fired on mourners at a funeral.
On the political front, opposition Syrian National Council leaders pressed the Arab League in Cairo to turn the Syria crisis over to the United Nations.
SNC chief Burhan Ghaliun met League head Nabil al-Arabi in the Egyptian capital and lobbied against extending the mission, SNC spokeswoman Basma Qadmani said.
The SNC wants "the transfer of the Syria file to the UN Security Council," spokesman Mohammed Sermini told AFP, accusing the Damascus regime of "committing genocide and crimes against humanity."
But the Arab League is expected to extend its mission, even boosting observer numbers, after foreign ministers are briefed on Sunday on the mission's first month in Syria.
An observer mission official, on condition of anonymity, has said its numbers would be almost doubled to 300.
Sunday's report will be delivered by the mission's chief, General Mohammed Ahmed Mustafa al-Dabi of Sudan, who believes his mandate needs to be strengthened, not scrapped, a League official said.
Deputy chief of operations Ali Jarush said Dabi is satisfied with its achievements so far and that "everything indicates the observer mission in Syria will be extended by a month."
"Dabi sees that in the last phase the necessary thrust (of the operation) was achieved after more monitors were deployed and fanned across 20 areas and after they were provided with equipment and logistics which they previously lacked," he said.
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But the SNC charged that Dabi's report will not be credible.
Addressing journalists, Ghaliun said he told Arabi that the conditions under which the observers were forced to work "do not allow it to present an objective report, reflecting the actual situation in Syria."
The League's staff were escorted around Syria by government troops.
Ahead of Sunday's Cairo meetings, the killing in Syria continued.
A roadside bomb on Saturday killed 17 detainees being transported in a prison truck in Idlib province in the northwest, the Observatory said.
State news agency SANA said "an armed terrorist group" attacked the vehicle in the Al-Mastouma area, "killing 14 prisoners and wounding 26 others."
The Observatory also reported people wounded in the attack.
Separately, nine government troops were killed during clashes with dissident soldiers near a military roadblock in the central city of Maaret Numan, the Observatory reported, citing a dissident.
One deserter was also killed in the clash, according to the group, which also said a member of the security forces died while fighting dissidents at Kfarnebel in Idlib's Zawiya mountains.
Security forces also killed three members of a "terrorist group" on Friday night as they tried to infiltrate the Tal Kala area from neighbouring Lebanon, SANA said.
The rebel Free Syrian Army (FSA), trying to boost coordination between disparate groups of dissident fighters, said on Saturday it feared the government would attack Zabadani, a rebel-held town northeast of Damascus.
Major Maher Nueimi, an FSA spokesman, said the rebel force did not have the necessary arsenal to confront the regime's troops directly, and that it was concerned about defending Zabadani's residents.
On Syria's maritime border with Lebanon, a 14-year-old Lebanese boy was shot and fatally wounded after gunmen opened fire on a fishing boat, his father and a local official told AFP.
Qatar has proposed that Arab troops be deployed in Syria, but Damascus vehemently rejected the proposal.
Syria's state Ath-Thawra daily on Saturday accused Qatar of being a "tool" of the United States that is trying to bring down President Bashar al-Assad's regime on orders from Washington.
"It is clear that Qatar... is trying to distance itself from Arab League and the report" that is expected to call for the renewal of the League's peace mission, the paper alleged.