"An improvised explosive device was placed close to a network of pipelines at the level of al-Fatiha, west of Kirkuk, causing a big explosion and huge fires that damaged the main pipeline running to Jihan and stopped exports," said Nasir Qasim, a logistics and security official with the state-owned company.
He said the attack occurred at about 6:00am (1400 GMT) in an area 120km west of Kirkuk.
The road connecting Kirkuk with the refineries in Biji to the west was cut off as emergency workers battled to extinguish the raging flames, with Iraqi police and national guard units, and occupation troops securing the area.
Firefighters for some time could not approach the pipeline due to the heat emanating in the area, our correspondent reported.
Sand barriers were also erected to contain the fires as thick black smoke covered the skies and could be seen all the way from Kirkuk.
The key artery was earlier
attacked in mid-July
An oil ministry spokesman in Baghdad declined to comment on the attack.
But a source from al-Shamal oil company told Aljazeera that the explosion would affect oil production a great deal.
The key northern artery only resumed work on Sunday carrying 200,000 barrels a day, after an attack in mid-July halted exports.
Until the end of June, the pipeline had been out of commission for about 10 months after a series of attacks.
Repeated attacks on Iraq's oil infrastructure have defied the interim government's efforts to increase exports. The bulk of Iraq's oil exports go through tanker terminals on the Gulf.
Exports from the southern oilfields have been running at up to 1.7 million barrels a day, but have suffered periodic disruption in recent months, some of it the result of attacks on pipelines.