BEIRUT — Syrian activists said fighters belonging to rival Islamic rebel groups are battling each other in the north and at least 12 have died.

The Britain-based Syrian Observatory for Human Rights said members of the al-Qaeda-linked Islamic State of Iraq and the Levant and another Islamic group clashed in the town of Maskaneh in the northern Aleppo province. Fighting started Tuesday morning after ISIL members detained a man to try him in an Islamic court they set up after driving President Bashar Assad’s forces from the area.

Over the past year, the ISIL has become one of the most influential groups on the opposition’s side in the country’s nearly three-year-old conflict. The infighting has weakening the battle to oust Assad.

Copyright 2013 The Associated Press.