Activists say Syrian warplanes have bombed a building in a suburb of the capital Damascus in the first airstrike since an internationally mediated ceasefire went into effect.
The attack and other violence casts further doubt on the chances that the four-day truce that began Friday will be a springboard for ending the civil war.
The Britain-based Syrian Observatory for Human Rights says eight people were killed and many others wounded in Saturday's airstrike in Arbeen. The area also has witnessed heavy clashes and intense shelling.
An amateur video posted by activists online shows a pile of rubble said to be from the airstrike.
The attack follows the detonation of two car bombs on Friday, just hours after the cease-fire took effect, which combined killed 13 and wounded 30.
Also on Saturday Syrian troops shelled rebel-held areas and clashed with anti-government gunmen in several parts of the country despite the ceasefire, while rebels and Kurdish neighborhood guards fought a rare battle in the embattled city of Aleppo that left nearly two dozen people dead, activists said.
The fighting in Aleppo's predominantly Kurdish neighborhood of Ashrafieh late Friday occurred a day after rebels pushed into largely Kurdish and Christian areas that have been relatively quiet during the three-month battle for the city.
Kurds say the rebels had pledged to stay out of their neighborhoods. Kurdish groups have for the most part tried to steer a middle course in the conflict between the rebels and the regime of President Bashar Assad. Some figures have allied with the rebels, others with Assad, and others have remained neutral.
The Observatory said 19 rebels and three Kurdish gunmen were killed in the clash that lasted several hours. A Kurdish official put the death toll at 10 Kurds, but had no figures for the rebels.
Kurds are the largest ethnic minority in Syria and make up around 10 to 15 per cent of the country's 23 million people. Most of them live in the northeastern Hasakeh province near the border with Turkey, but large neighborhoods in Aleppo as well as the capital Damascus are Kurdish-dominated.
After the anti-government uprising began in March last year, both the Syrian government and opposition forces began reaching out to the long-marginalized minority whose support could tip the balance in the conflict.
Kurds have long complained of neglect and discrimination. Assad's government for years argued they are not Syrians, but Kurds who fled from Iraq or neighboring Turkey. But the Kurds are also leery of how they would fare in a Syria dominated by the large Sunni Arab rebel movement.
Early on in the revolt, Assad ceded ground on a major Kurdish demand, granting citizenship to some 200,000 who were registered as aliens before. Mindful of provoking the Kurds, security forces have refrained from using deadly force to put down protests in Kurdish regions, and residents say they have largely abandoned their posts there.
In other violence, the Observatory and the Local Co-ordination Committees reported shelling and shooting Saturday mostly in Aleppo, the eastern region of Deir el-Zour, Daraa to the south and suburbs of the capital Damascus.
Syria mediator Lakhdar Brahimi, the UN-Arab League envoy, had mediated a four-day ceasefire that began Friday to mark the Muslim feast of Eid al-Adha.
"The ceasefire collapsed nearly three hours after it went into effect," said Rami Abdul-Rahman, who heads the Observatory. "The only difference is that the fighting is less widespread and regime has not been using its air force since the ceasefire began."
Also Saturday, state-run Syrian TV reported that rebels violated the ceasefire by detonating a car bomb outside an Assyrian Christian church in the eastern city of Deir el-Zour near the border with Iraq.
A Syrian official, who spoke on condition of anonymity in line with regulations, said part of the church was damaged but the blast caused no casualties.
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