Syrian regime troops used tear gas to try to disperse a mass funeral attended by thousands of people who took to the streets of Damascus to mourn slain protesters, a rights group said.
The protests were staged after deadly blasts rocked Damascus and the country's second city Aleppo earlier on Saturday, the Britain-based Syrian Observatory for Human Rights said.
"Syrian regime forces used tear gas to disperse people attending the funerals of the Kfar Sousa martyrs and calling for the fall of the regime," the Observatory said.
The violence came just two days before a scheduled parliamentary election in Syria, where President Bashar al-Assad's regime has been trying to crush an uprising since March 2011.
One explosion hit a car wash as a bus was passing in a suburb of Aleppo, the country's northern commercial hub, killing at least five people, Rami Abdel Rahman of the Syrian Observatory told AFP in Beirut.
The state-run SANA news agency reported three deaths in Aleppo -- including a 10-year-old boy -- and 21 others wounded, two of them critically.
Pictures of the bombing released by SANA showed extensive damage to buildings and cars.
The Observatory later said at least 15 people were killed across the country on Saturday.
They included a civilian and two rebel fighters in an ambush in Saraqeb, a town in the northwestern province of Idlib, and an army officer in Aleppo.
Two blasts also hit Damascus, Abdel Rahman said, with three soldiers wounded in one of the attacks. Television footage showed a mangled car destroyed by one of the explosions.
Abdel Rahman accused the regime of launching the attacks to stop funerals a day after the security forces killed 30 anti-regime protesters, including nine in the Kfar Sousa and Tadamon districts of Damascus.
The Observatory says more than 600 people have been killed nationwide since a tenuous truce went into effect April 12.
Also in Damascus, troops opened fire in the central neighbourhood of Barzeh, as they carried out multiple raids and arrests, the watchdog said.
Despite the violence, mourners took to the streets of Kfar Sousa, just under a kilometre (less than a mile) from the prime minister's office, as shown in an amateur broadcast posted online by activists.
"The funerals will show the regime that Damascus is not a neutral city as they pretend," the opposition bloc Syrian National Council said in a statement.
Internet footage showed one mass funeral-turned-protest in Kfar Sousa after Friday's killings there.
"Syria wants freedom!" and "God is great!" chanted protesters. "We salute the (rebel) Free Syrian Army," read one slogan painted on a wall in Kfar Sousa.
Holding up pictures of some of the nine people the security forces killed in Damascus on Friday, mourners also denounced sectarianism, chanting that "the Syrian people are one."
Hundreds of people also took to the streets to honour the dead in the Tadamon area, video footage posted online by activists showed.
An anti-regime protest was also staged in the Druze-majority area of Sweida in the south, according to a video uploaded to YouTube by activists.
It was not immediately possible to verify the authenticity of such footage.
The Observatory reported that unidentified gunmen killed an official of the ruling Baath party in Idlib province.
Six people were killed in shelling by regime forces in Homs province, central Syria, it said, after a man was reportedly killed in a rocket attack on the outskirts of the rebel-held town of Rastan.
And regime troops arrested human rights lawyer Saad Mustafa al-Khash in Masiaf in Hama province, the Observatory said.
Part of a six-point blueprint for peace, the shaky ceasefire deal was brokered by UN and Arab League envoy Kofi Annan, whose office said on Friday that his plan was still "on track."
Under it, Assad's government agreed to withdraw its troops and heavy weapons from urban areas, allow peaceful demonstrations, and to release prisoners.
"The Annan plan is on track and a crisis that has been going on for over a year is not going to be resolved in a day or a week," Annan's spokesman in Geneva, Ahmad Fawzi, told journalists.
On Saturday, SANA reported that authorities had freed 265 detainees "involved" in the uprising "who do not have blood on their hands."
At least 4,000 prisoners had now been freed since November, it said.
The agency also reported deadly clashes on the border with Turkey as troops foiled an infiltration attempt by "an armed terrorist group."
The Observatory estimates that more than 11,000 people have been killed in the 14 months since the outbreak of the revolt.
An Islamist group calling itself Al-Nusra Front meanwhile claimed responsibility for a deadly suicide bombing last month near the Syrian city of Hama, the SITE Monitoring Service said Saturday, citing an online statement.
Al-Nusra Front named the bomber as Abu Bakr al-Hamawi, and said he detonated his explosives-laden vehicle at a restaurant where Syrian security forces were dining on April 20.
His intention was to target military staff who took part in massacring protestors in the town of Latamnah, said the statement.© ANP/AFP