Syrian activists say at least 21 people have been killed in clashes throughout Syria Saturday.

The British-based Syrian Observatory for Human Rights said the majority of the deaths occurred in the flashpoint central city of Homs and in the restive Idlib province in the northwest.

The clashes came as thousands of supporters of President Bashar al Assad joined a funeral ceremony in Damascus for 26 people killed in a bomb attack a day earlier.

The government called the devastating explosion Friday, which also wounded more than 60 people, a “terrorist” attack and accused opposition groups of being behind the killings. It also vowed to “strike back with an iron fist” against the perpetrators.

But opposition activists deny any involvement in the bombing and have suggested the authorities staged the explosion to create a backlash against those calling for a government removal.

Most of those killed in the attack Friday appeared to be policemen riding on a bus that was shattered by the blast. Syrian state media quoted an Interior Ministry official as asserting that a male suicide bomber triggered the blast in the central Midan district, but few other details were available.

Opposition activists said the Syrian regime's crackdown on protesters continued in several parts of the country late Friday in which 17 civilians were killed.

Arab League ministers are to meet in Cairo Sunday to review the work of an observer mission the league has sent to Syria two weeks ago. The observers were tasked with finding out whether the Assad government has lived up to its pledge that its long-running crackdown on civilian protesters was at an end.

Mr. Assad has pledged to withdraw security forces from cities, release political prisoners and allow anti-government protests. Government reports of mass prisoner releases have not been verified, in part because almost all foreign journalists are barred from access to the country.

A global, online activist group that supports “people-power” movements worldwide, Avaaz, says nearly 7,000 people were killed since March 2011, when the Syrian unrest began. Avaaz says its casualty count was confirmed through contacts with multiple sources in Syria.

The United Nations estimates 5,000 people have been killed in Syria, while the Damascus government accuses armed terrorists of driving the revolt and killing 2,000 security personnel.