A deadly blast rocked a Damascus suburb, killing two security forces members, among 10 people killed across Syria on Friday, said the Syrian Observatory for Human Rights.
The bloodshed came as people took to the streets to demonstrate against the regime of President Bashar al-Assad following weekly Muslim prayers, the main day of protests in the 15-month uprising.
An AFP photographer said the blast in the capital's Qudssaya neighbourhood tore a car to shreds and damaged a military bus -- the reported target -- as well as some nearby residential buildings.
Elsewhere, an explosion in front of a police station in the northwestern city of Idlib killed five people, including another two more members of the security forces, said the Britain-based Observatory.
"It was a powerful explosion that destroyed the facade of the building," said the watchdog, which also reported that a civilian was shot dead at Kfar Nebbol in the same province.
In other violence, troops battled to take back the rebel bastion of Khaldiyeh in the central city of Homs, shelling the district, the Observatory said.
Khaldiyeh in the north of the city has been pounded intermittently since Friday morning "at a rate of five shells a minute," the Observatory said.
In the southern province of Daraa, cradle of the uprising, the head of a rebel "brigade" was killed at Basr al-Sham and a sniper shot dead a civilian in Mahajja, said the Observatory.
At least 58 people were killed on Thursday across Syria, where the crisis may "spiral out of control," UN-Arab League envoy Kofi Annan told the UN Security Council, unless more pressure is put on Assad.
Anti-regime activists had called for fresh demonstrations on Friday, under the slogan "Revolutionaries and traders, hand in hand until victory," in an attempt to convince the middle classes in Damascus and the northern city of Aleppo to join the uprising that erupted in mid-March 2011.
People emerged from mosques to demonstrate in Kfar Zita, in the central Hama province, chanting: "We don't want peace. We want bullets and Kalashnikovs!"
A convoy of UN monitors trying to reach the central village of Al-Kubeir on Thursday to investigate the slaughter of at least 55 civilians in the small Sunni farming area was shot at, the Observatory said.