The pipeline, which connects oilfields in Dibis with the northern city of Kirkuk, 35km to the southeast, was destroyed late on Friday, an official of the state-run North Oil Co said. He said it would take at least four days to repair the line.
Fighters often target Iraq's oil infrastructure, cutting exports and denying the country funds.
Also on Saturday, fighters detonated a roadside bomb in the west of the city, killing two civilians who were passing by in a vehicle at the time. Their slumped bodies could be seen in a small white car littered with holes from flying shrapnel, its windshield smashed by the blast.
It was not clear what the target of the attack was. US Lt-Col Clifford Kent said a US tank was nearby at the time, but it was not damaged.
"While we were going to work, we just arrived near those tanks, the blast occurred. And as you see, blood soaked us for doing nothing," Muhammad al-Dulaimi told reporters
In the northern city of Mosul, residents found the body of Raida Muhammad Wajih Wazan, a presenter for the local state TV station, who had been missing since 20 February when she was kidnapped by masked fighters, her husband Salim Sad-Allah said.
Her corpse was found on Friday. She had been shot in the head.
South of Baghdad, a car bomb exploded near a convoy of Iraqi National Guard troops in Iskandariya, witnesses said. No casualties were reported.
Iraqi security personnel are very
often targeted by armed fighters
Separately, an Iraqi soldier was killed and five others injured on Saturday when a car bomb exploded as an Iraqi military convoy passed through al-Musayib area in southern Baghdad, Aljazeera learned.
In another incident on Saturday, two Iraqis were killed and seven others injured during clashes between fighters and US forces in Ramadi.
US forces have cordoned off the eastern parts of the city, calling on residents through loudspeakers to cooperate with them in what they say is an effort to force Abu Musab al-Zarqawi out of the city.
Separately, US forces and the Iraqi army launched a raid and search operations into areas near Falluja, Aljazeera learned.
US forces were deployed in al-Saqlawiya and Amiriyat Falluja towns and nearby villages. They arrested Shaikh Ahmad Abd Allah al-Muhammadi, a member of the Association of Muslim Scholars in Iraq, and a number of residents.