Baghdad: Sunni militant groups have attacked Iraq's largest oil refinery in Salahudin province Wednesday, sparking a huge fire, a provincial police source said.

Hundreds of gunmen, including the militants linked to the Islamic State in Iraq and Levant (ISIL), an Al Qaeda offshoot, waged an attack at dawn on the refinery compound in Baiji city from several directions with machine guns and mortar rounds, the source told Xinhua on condition of anonymity.