Gunmen on Saturday stormed Iraq's largest oil refinery in Salahudin province and killed two workers before they bombed the refinery units, a police source said.

"Unidentified gunmen stormed the oil refinery and shot dead an engineer and a guard before they planted bombs to several units in the refinery and blew them up causing huge fire," the source from the police of Salahudin province told Xinhua on condition of anonymity.

"The huge fire caused the work to completely stop at the refinery which located some 200 km north of Baghdad," the source said.

Iraqi security forces and top officials of the province rushed to the scene, as teams of firefighters and many fire engines reached there to put out the fire, where column of thick and black smoke could be seen from long distance pouring into the sky, the source added.

The refinery is run by the Iraqi North Refineries Company, which is affiliated to the country's Oil Ministry. The refinery has a capacity of 300,000 barrels per day.