Syrian regime troops used tear gas on Saturday 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.
"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 Britain-based Syrian Observatory for Human Rights said.
The protests were staged after deadly blasts rocked Damascus and the country's second city Aleppo earlier on Saturday, 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, said Rami Abdel Rahman of the Syrian Observatory.
At least five people were killed in the blast, he told AFP in Beirut.
The state-run SANA news agency reported three deaths in Aleppo, and said 21 others were wounded, two of them critically.
The dead included a 10-year-old boy killed "in the explosion of a booby-trapped passenger car parked by a terrorist outside a car wash," it said.
Pictures of the bombing released by SANA showed extensive damage to buildings and cars.
Aleppo has been the scene of escalating violence, including a regime raid on the university, according to the Observatory.
It later said at least 15 people were killed across the country on Saturday, including 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, one "inside the city, and the other hit the periphery" where three soldiers were wounded.
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 during a tenuous truce that went into effect April 12.
Also in Damascus, troops opened fire in the central neighbourhood of Barzeh, as they carried out multiple raids and made arbitrary 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.
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"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.
Elsewhere in Syria, the Observatory reported that unidentified gunmen assassinated 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.
Regime troops also arrested human rights lawyer Saad Mustafa al-Khash in Masiaf in Hama province, the Observatory said, calling him "a defender of the peaceful movement in Syria."
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 spokesperson in Geneva, Ahmad Fawzi, told journalists.
On Saturday, SANA reported that authorities have freed 265 detainees "involved" in the uprising "who do not have blood on their hands."
At least 4,000 prisoners have 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."
Overall, the Observatory estimates that more than 11,000 people have been killed in the 14 months since the outbreak of the revolt.