BEIRUT - Two car bombs set off by Islamic State insurgents killed at least 31 people in northern Syria including a senior rival fighter from al Qaeda's Nusra Front, a group monitoring the war said on Wednesday.
Islamic State, which has captured wide areas of Syria and Iraq, has frequently fought rival armed groups but in some cases has also coordinated with them, complicating the four-year insurgency against Syrian President Bashar al-Assad.
The bombs were detonated on Tuesday in the town of Marea, around 40 km (25 miles) north of Aleppo city, targeting the headquarters of rival insurgents and another area where they were operating, according to the Britain-based Syrian Observatory for Human Rights.
Rebels say Islamic State halted its western advance last summer at Marea, which has become a battleground for rival forces. Roads running north from Aleppo provide important rebel supply lines into the city, which is divided between Syrian government forces and various insurgent groups.
Among the dead in Tuesday's bombings were a "local emir"from Nusra Front, and two leaders of insurgent Islamist factions in the area, the Observatory said.
It collects its information from a network of sources on the ground. Nusra Front said online that one of its leaders was killed in an Islamic State car bomb attack in the area and posted a picture of what appeared to be his body on a blanket.
An Islamic State news bulletin posted online said that one its members set off a car bomb in the Marea area.
Insurgent groups including the Nusra Front took up arms against Islamic State early last year.