Syrian warplanes have bombed a building in a Damascus suburb, killing at least eight people in the first airstrike since an internationally mediated cease-fire went into effect, activists have said.

The attack came a day after car bombs and clashes left 151 dead, according to activist tallies, leaving the four-day truce that began Friday at the start of a major Muslim holiday in tatters.

The rapid unravelling of the effort to achieve even a temporary peace marked the latest setback to ending Syria's civil war through diplomacy after months of failed efforts.

The Britain-based Syrian Observatory for Human Rights said eight people were killed and many others wounded in the airstrike in Arbeen, a suburb of the capital. The area also has witnessed heavy clashes and intense shelling.

An amateur video posted by activists online showed a building that was turned into a pile of rubble said to be from the airstrike.

The videos appear consistent with AP's reporting in the area.

In the north, rebels and Kurdish neighbourhood guards fought a rare battle late Friday in the embattled city of Aleppo that left 30 people dead, activists said.

In all, 151 people were reported killed on Friday, including 11 in a car bomb in a residential area of Damascus, on par with the daily death tolls preceding the cease-fire.

Shelling and clashes resumed Saturday nationwide.

A car bomb parked behind an Assyrian church near a military police compound and a military court went off today killing five people in the eastern city of Deir el-Zour, according to the Observatory.

Military forces that rushed to the site of the blast then came under rebel fire, and three soldiers were killed, it said.

State-run TV denied the blast caused any casualties.

Nobody claimed responsibility, but the attack was similar to those staged in the past by a radical Islamic group fighting on the rebel side, Jabhat al-Nusra, which has rejected the cease-fire outright.

The Observatory also said 30 rebels and Kurdish gunmen were killed in clashes that broke out in Aleppo's predominantly Kurdish neighbourhood of Ashrafieh late Friday.

A Kurdish official put the death toll at 10 Kurds, but had no figures for the rebels.

Rebels made a push Thursday into largely Kurdish and Christian areas that had been relatively quiet during the three-month battle for Syria's largest city.

Kurds say the rebels had pledged to stay out of their neighbourhoods.

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.

Mohieddine Sheik Ali, head of the Kurdish Yekiti party, said the clashes broke out after rebels entered Ashrafieh, violating "a gentlemen's agreement" not to go into Kurdish areas in Aleppo.

He said 100,000 Kurds live in Ashrafieh and many in the nearby Sheik Maksoud area. Sheik Ali said tens of thousands of Arabs have also fled to these areas to escape the violence in other parts of Aleppo.

The Observatory said the clashes led to a wave of kidnappings between the two groups, but did not provide further details. Pro-government news websites also reported the clashes.

Kurds are the largest ethnic minority in Syria, making up around 10% to 15% of the country's 23 million people.

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. But they are also leery of how they would fare in a Syria dominated by the large Sunni Arab rebel movement.

In other violence, the Observatory and the Local Coordination Committees also reported shelling and shooting today in Aleppo and Daraa to the south.

Syria mediator Lakhdar Brahimi, the UN-Arab League envoy, had mediated a four-day cease-fire that began Friday to mark the Muslim feast of Eid al-Adha.

"The cease-fire collapsed nearly three hours after it went into effect," said Rami Abdul-Rahman, who heads the Observatory.

In Lebanon, the leading LBC TV said Lebanese journalist Fidaa Itani, one of its employees covering Syria's civil war, was detained by the rebels and is being held in the town of Azaz near the Turkish border.

The station quoted a local rebel leader in Azaz, Abu Ibrahim, as saying that rebels suspected Itani after he filmed many videos of rebels operations in Aleppo. Itani's Lebanese cell phone was closed when The Associated Press tried to reach him.

The area also was the site of the May kidnapping of 11 Shiite Lebanese pilgrims who were on their way home from Iran. Two have been released while rebels say they will hold the others until Sheik Hassan Nasrallah, the leader of Lebanon's militant Hezbollah group, apologizes from the Syrian people for supporting Assad.