BAGHDAD, Dec 18: Saboteurs blew up Iraq's northern export pipeline for the second week in a row on Saturday, halting oil flows to Turkey's Ceyhan port, oil officials said.

Iraq's oil infrastructure has suffered five attacks in 24 hours after a voice identified as Al-Qaeda leader Osama bin Laden's ordered followers to sabotage the West's key supplies.

Bombers also targeted a US patrol in Mosul, killing one Iraqi and wounding eight, just 24 hours after four Turkish security guards were mown down in an ambush in the main northern city.

The violence came as an Iraqi special tribunal announced that it had held its first investigative hearings of former regime officials, beginning with Ali Hassan al-Majid, better known as "Chemical Ali" for his role in the chemical bombing of Halabja, a Kurdish town, in 1988 which killed 5000 civilians according to UN estimates.

The pipeline runs from the Kirkuk oil fields to the IT-1A storage tanks near Baiji, where oil accumulates before it is pumped further north to Ceyhan.

Storage tanks at IT-1A were full before the attack, but technical problems have been hampering pumping to Ceyhan, one official said.

The northern pipeline, which can carry around 500,000 barrels per day (bpd), was also attacked on Dec 10. Exports through Turkey have been volatile since, lowering the level of Iraqi crude oil stored at Ceyhan.

Another domestic oil pipeline was hit near Baiji on Saturday, the latest in attacks that have crippled operations of refineries and helped to create severe shortages of fuels, especially in Baghdad.

There were two blasts on pipelines Saturday and three late Friday, all of them in restive Sunni areas around the capital or in north-central Iraq, officials said.

The saboteurs struck pipelines serving both Iraq's northern and southern oil fields and halted the flow of crude to Baghdad's Daura refinery, interrupting the production of refined fuel, the oil ministry said.

In Mosul, one Iraqi was killed and eight wounded by a bomb targeting a US patrol, medics and a witness said. A US spokesman said the blast hit a school bus.

The attack came just a day after four Turkish security guards were gunned down in an ambush in the city's Yarmuk neighbourhood.

"Armed men made the passengers get out of the cars, lie on the ground, machine-gunned them and cut off the head off one of them," Muhammet Tahir, an official of the Turkmen Front in Mosul, was quoted as telling the Turkish press agency DHA.

One of the guards and a driver survived the attack and returned to Turkey, while two other guards made it safely to the embassy in Baghdad, the foreign ministry said.

"Our authorities are investigating the matter and trying to obtain more information from the Iraqi interim government and local officials."

In Mosul, US Lieutenant Colonel Paul Hastings, spokesman for Task Force Olympia, said that troops had recovered three male bodies evidently killed earlier during the day in a rebel attack.

"All three had bullet wounds. The fourth, reported by news agencies, was not recovered," he said.

ELECTION OFFICES HIT: Two people were killed and eight were wounded, including six National Guards, when mortars landed on an election office in Dujail, 50km north of Baghdad. It is one of many around the country registering and educating voters.