Unknown assailants set off a fire near a vital oil pipeline in northern Iraq, raising concerns that the heat could damage the line, an oil official said Tuesday. Firefighters were trying to put off the fire which erupted late Monday after someone set ablaze a hole in the ground filled with oil that had leaked out during previous attacks, said a Northern Oil Co. official who spoke on condition of anonymity. He said the fire, in an area about 70 kilometers (43.5 miles) southwest of Kirkuk, could cause nearby pipelines to explode. They include the line leading from the northern oil fields to the Turkish port of Ceyhan, a principal export route for Iraqi oil. Kirkuk is about 290 kilometers (180 miles) north of Baghdad.