BEIRUT —Syria launched a series of airstrikes targeting a stronghold of the Islamic State extremist group on Saturday, killing at least 29 people, most of whom died when one of the missiles slammed into a crowded bakery, activists said.

The eight airstrikes smashed parts of buildings, set cars alight and crushed people under rubble in the northeastern city of Raqqa, which is ruled by the extremist group, according to video of the aftermath uploaded to social media networks.

At least 20 civilians were killed, alongside nine Islamic State fighters, said the Britain-based Syrian Observatory for Human Rights. Most of the civilians were killed after at least one strike hit the Andalous bakery on a busy street, and the death toll was likely to rise, said the Observatory, which obtains its information from a network of activists on the ground.

The airstrikes were also reported by an activist who uses the name Abu Ibrahim and is a member of a media collective called “Raqqa is being silently slaughtered.” He fled Syria fearing for his safety and asked that his current place of residence remain anonymous.

Another group, the Raqqa Media Center, uploaded video of the aftermath, which appeared to be genuine and was consistent with AP reporting of the event.

Abu Ibrahim said the local morgue was packed with charred bodies, making identification difficult. He and the Observatory said at least eight members of one family were killed.

Other strikes hit a government finance building that the Islamic State used as its headquarters and another building used as a jail, Abu Ibrahim said.

It has been virtually impossible for journalists to visit Raqqa, a city of some 500,000 people on the banks of the Euphrates River, since the town fell to the Islamic State group earlier this year.

The group routinely abducts reporters and recently beheaded two American journalists in response to U.S. airstrikes against the militants in Iraq.

The Syrian government strikes were part of an uptick of military action against the Islamic State group since it swept into neighboring Iraq, seizing northern and western swaths of that country and declaring a proto-state straddling the border.

Syrian President Bashar Assad’s government has also suffered heavy losses against the Islamic State group, which killed hundreds of soldiers and pro-government fighters in recent months as it overran oil fields and military bases.

There was no immediate government comment on the airstrikes.

In a separate incident, a Syrian military helicopter dropped a barrel bomb on a bus station in a rebel-held neighborhood of the northern city of Aleppo on Friday, killing at least 15 people, according to the Observatory and Aleppo-based activist Zein al-Rifai.

Al-Rifai and the Observatory said residents were still pulling out bodies from under the rubble on Saturday.

It wasn’t immediately clear why the station, in the otherwise largely-abandoned, bombed-out neighborhood of Haydariyeh was targeted.

The government has carried out hundreds of raids in which it has dropped explosives-filled barrels on Aleppo in a bid to flush rebels out of Syria’s second largest city and onetime commercial hub.

Activists say the so-called barrel bombs have killed thousands of civilians, and international rights groups have condemned the tactic, saying the bombs cannot be precisely targeted.