|Syrian army has vowed to hunt down and arrest opponents of President Bashar al-Assad [Al Jazeera]
The Syrian government says 10 civilian workers have been killed by an "armed terrorist gang" in a bus ambush near the city of Homs.
The official state news agency carried images of the bus that it said was returning from Lebanon on Sunday when it was attacked.
The agency quoted a doctor at a hospital in Homs as saying the victims had been shot at close range.
The authorities have blamed armed gangs backed by foreign powers for the violence during Syria's seven-week uprising against the authoritarian rule of president Bashar al-Assad.
But human rights campaigners cast doubt on the incident near Homs, the country's third largest city, where army and security presence is heavy.
They said scores of unarmed protesters, including a 12-year-old child, had been killed by security forces in the city, and that no independent observers were allowed to verify official accounts.
Troops backed by tanks entered residential areas in Homs and Tafas, a town in the south, early on Sunday amid the sound of gunfire, activists said.
Night rally attacked
In the eastern city of Deir al-Zour, a witness said Syrian forces killed at least two unarmed demonstrators on Sunday when they opened fire on a night rally.
"There are two bodies on the ground and no one can reach them. There is still gunfire and people are fleeing the scene," the witness told Reuters from the Old Airport district of the tribal city.
In-depth coverage of escalating violence across Syria
Deir al-Zour, the centre of Syria's oil production, has been witnessing rallies that have attracted up to 4,000 people each night since security forces killed four pro-democracy protesters on Friday, residents said.
Demonstrators earlier tore down a golden statue of Assad's elder brother, Basil, who had been the presumed heir to the former president, Hafez al-Assad.
In the coastal city of Baniyas, two pro-democracy leaders and at least 250 people have been detained since army units stormed the city on Saturday, a rights organisation said.
The UK-based Syrian Observatory for Human Rights said Sheikh Anas Airout, the preacher at the city's main Rahman mosque, and prominent activist Bassam Sahyouni were seized by security forces.
Rami Abdul-Rahman, the observatory's director, said a 10-year-old boy was also arrested in what appeared to be a move designed to punish the child's parents.
'City of ghosts'
"Baniyas is a city of ghosts today, it's empty and totally isolated from the rest of Syria," Ammar Qurabi of Syria's National Organisation for Human Rights said.
"There's a de facto curfew and people are not going out," he said.
Activists said four women were killed on Saturday as they were demonstrating along with 150 others on the main coastal highway from Marqab village, near Baniyas, calling for the release of detainees.
In Deraa, the southern city where the military has been deployed for two weeks to quell unrest, security forces allowed people to come out for few hours on Sunday to buy essentials but then imposed a curfew, according to activists.
Syrian authorities have banned foreign media from reporting from the country. As a result of these restrictions, Al Jazeera cannot independently verify these figures.
Meanwhile, concerns remain for the welfare of Dorothy Parvaz, an Al Jazeera journalist, who has not been heard from since she arrived in the capital, Damascus, more than a week ago.