The latest deadly violence came one day after mourners in the southern town of Daraa, epicentre of more than three weeks of pro-democracy protests, buried around 20 demonstrators killed by security forces.
In Banias, the civilian toll was at least four dead and 17 wounded on Sunday from shooting by security forces in the neighbourhood of Ras al-Nabee, where the Al-Rahman mosque has been a focal point of anti-regime demonstrations.
"The army and security forces and gunmen besieged the town from all sides and fired without interruption for several hours," a university professor told AFP.
"(President) Bashar al-Assad is sending us a message: punish those who dare demand freedom with death," he said.
The gunfire came from the Alawite neighbourhood of Al-Quz, two witnesses said, with one adding that it was "a real massacre with snipers shooting to kill."
A rights activist said the shots were aimed at the mosque and left "four dead and 15 wounded."
State news agency SANA said that a security officer was killed and another critically wounded in apparent retaliation.
"At 4:00 pm, an army unit between Latakia and Tartus was ambushed by an armed group by the roadside in trees and buildings," the agency quoted an official as saying.
"One officer was killed and another critically wounded, and several soldiers were also wounded. The armed forces are hunting down the elements of this armed group to arrest them and bring them to justice."
Banias residents on Saturday had reportedly agreed to stage a rooftop protest at 10:00 pm to call for the fall of the regime, but by 8:30 all land lines and cell phones were cut.
A witness said residents had set up checkpoints to guard their neighbourhoods against unrest.
All of the witnesses and activists who spoke to AFP requested anonymity, citing security concerns.
Five people had already been wounded earlier on Sunday in Banias in a drive-by shooting reportedly by plainclothes government agents in the Mediterranean town, according to a witness.
Seven cars "carrying people sent by the regime arrived in front of the Abu Bakr al-Sidiq mosque and their occupants opened fire" during morning prayers, the witness said.
The perpetrators quickly took flight, although witnesses were able to record the licence plates of some of their vehicles.
"The people behind this shooting are regime thugs and their names are known to us," the witness said, and added that peaceful demonstrations had also been held in Banias on Saturday afternoon.
Anti-regime demonstrations and clashes with security forces raged across the country on Friday leaving 28 dead, including 26 in Daraa, according to an updated toll by six Syrian rights groups.
And on Saturday security forces shot at protesters in Daraa, wounding two people, an activist said, as a huge crowd buried the dead from the previous day.
The organisations on Sunday voiced their "concern at the determination of Syrian authorities to continue violating essential rights and freedoms."
An unprecedented opposition movement erupted in Syria on March 15 challenging the regime of Assad, who has been in power since 2000, to introduce major political reforms.
Assad, who has made only one public address since the start of unrest, on Sunday told Bulgaria's visiting foreign minister that "Syria was on the road to general reforms," SANA reported.
Since the political unrest erupted, the authorities have been pinning responsibility for protest-related violence on "armed groups," and the interior minister warned on Saturday that he would act firmly.
Assad last month ordered a legal committee to draft new legislation to replace emergency laws, in force since 1963, which give security services great leeway to crush dissent.
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