"The pipeline linking the Baiji refinery to that of Dura, in the capital, was sabotaged west of the city of Samarra," a local police officer said.
He said the sabotage on Saturday was carried out with a 10kg explosive charge on one of a cluster of eight pipelines bringing oil to the capital from the Baiji refinery, about 190km north of Baghdad.
Baiji refinery official Majid Mamnun confirmed the attack and added that the repairs would take up to a week.
A similar attack was perpetrated in the same area on 2 February.
Relentless attacks on the country's oil industry by fighters opposed to foreign troops have cost Iraq $7 billion to $8 billion in exports since the March 2003 US-led invasion.