BEIRUT (Reuters) - Around 95 captives have escaped a prison run by the Islamic State in Iraq and Syria (ISIS) in northern Syria, a group monitoring the war said on Tuesday, saying the escapees included about 30 Kurdish fighters.

The jailbreak happened in the town of al-Bab, 30 km south of the Turkish frontier, the Britain-based Syrian Observatory for Human Rights said.

ISIS, an Al-Qaeda offshoot, controls tracts of territory across northern Syria and runs its own prisons, courts and other facilities in what it describes as an Islamic caliphate extending into Iraq.

Kurdish fighters backed by US-led air strikes have been trying to drive back ISIS across northern Syria.

The escapees also included Syrian civilians and members of Islamic battalions opposed to the more hardline ISIS, the Observatory said.

ISIS has put the town on high alert and has been using loudspeakers to tell citizens to capture the escapees, the Observatory said, citing people on the ground.

Al-Bab was the site of ISIS infighting over the weekend when several of its members broke out of another jail in the town and tried to head for the Turkish border.

The group, which included mainly European fighters, was stopped by other ISIS members in clashes that killed at least nine, the Observatory said.