BEIRUT (AP) -- A Syrian government air raid struck a high school in a rebel-held city in the country's north on Sunday, killing at least 12 people, most of them students, activists said.

The airstrike took place in the city of Raqqa, which is located on the Euphrates River and is the only provincial capital under rebel control in Syria's civil war, the Britain-based Syrian Observatory for Human Right said. President Bashar Assad's regime has relied heavily on its air force to strike opposition-held areas, including Raqqa.

The attack appeared to hit the yard in front of the school early Sunday morning, which is the first day of the work week at public schools in Syria.

Observatory director Rami Abdul-Rahman said at least eight of the dead were students, and that the death toll is likely to rise because many of the wounded are in critical condition.

Amateur videos posted online showed at least nine bodies, some of them missing limbs, lying on pockmarked-pavement strewn with rubble. At least four of the bodies appeared to be of young people. Another video shows pools of blood on the ground and a concrete-block wall destroyed in the bombing.

The videos appeared genuine and corresponded to other AP reporting of the events depicted.