Blasts rocked Syria's capital and second city on Saturday, killing several people, a watchdog said, accusing the government of carrying out the attacks to prevent funerals for anti-regime protesters.
The violence came just two days before a scheduled parliamentary election in Syria, where the regime of President Bashar al-Assad has been trying to crush an uprising since March last year.
One explosion went off in a car wash just as a bus was passing by in a suburb of Aleppo, the country's commercial hub and second-largest city in the north, said Rami Abdel Rahman of the Syrian Observatory for Human Rights.
At least five people were killed in the blast, he told AFP in Beirut.
Two blasts also hit Damascus, Abdel Rahman said on the telephone from Britain. "One explosion occurred inside the city, and the other hit the periphery" where three soldiers were wounded, he added.
Television footage showed a mangled car destroyed by one of the explosions that tore through a street of the capital.
Abdel Rahman accused the regime of carrying out the attacks to stop funerals a day after the security forces killed 30 anti-regime protesters, including nine in the Damascus districts of Kfar Sousa and Tadamon.
"This is the highest death toll we have seen inside Damascus" since a United Nations-backed ceasefire came into effect on April 12, added Abdel Rahman, whose group says more than 600 people have been killed nationwide during the tenuous truce.
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.
But despite the bombings and other violence, thousands of mourners took to the streets of Kfar Sousa, as shown by a live amateur broadcast posted online by activists.
Opposition bloc the Syrian National Council had called on the UN observers to visit Kfar Sousa and Tadamon, "where the funerals of the martyrs killed Friday will be held."
"The funerals will show the regime that Damascus is not a neutral city as they pretend," it said in a statement.
Also on Saturday, the Observatory reported unidentified gunmen assassinated an official of the ruling Baath Party on the outskirts of northern Idlib.
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Part of a six-point blueprint for peace, the ceasefire deal was brokered by UN-Arab League envoy Kofi Annan, whose office said Friday that his plan was "on track."
Under the plan, the Assad government agreed to withdraw its troops and heavy weapons from urban areas and allow peaceful demonstrations.
"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 Friday.
"There are signs on the ground of movement, albeit slow and small.
"Some heavy weapons have been withdrawn, some heavy weapons remain. Some violence has receded, some violence continues. And that is not satisfactory, I'm not saying it is," he said.
On Friday, protesters had emerged from mosques after weekly prayers across the country, calling for Assad's ouster, said the Observatory.
Among the casualties were a couple and their child shot dead in Aleppo, scene of a bloody regime raid the day before in which four university students died.
Another 200 students were arrested in what the Observatory said could prove a turning point of the uprising in the northern city, largely spared by the violence so far.
Troops also shot at demonstrators in various other cities and towns, activists said.
Opposition activists had called for the protests under the rallying cry: "Our commitment (to the revolution) is our salvation."
Anti-regime demonstrations have been staged after prayers each Friday since the revolt against Assad's iron-fisted rule erupted.
An activist video posted on YouTube showed demonstrators in Irbin, a town in Damascus province, carrying a banner that read: "Dear observers, thank you for your visit and goodbye."
"One year of killings and you still need observers to know the truth? Enough lies," read another banner carried by protesters in a neighbourhood of the capital.
Overall, the Observatory estimates that more than 11,000 people have been killed since the outbreak in March last year of the revolt against Assad's regime.