The attack on Wednesday also started a fire that burned for well over an hour.

Elsewhere, a car bomb exploded outside the headquarters of the provincial police force in Samawah, 240km south of the capital, Baghdad, police said. Two people were wounded in the blast, which set two other vehicles ablaze, a hospital official said.

Fighters struck the logistics base on the edge of Baghdad's airport at about 8:15am, said Lieutenant Colonel Richard Rael, their commander. The base is operated by the New Mexico Army National Guard's 515 Corps Support Battalion.

A pall of black smoke hung over the airport for an hour after one of the 82 mm mortar rounds struck a petroleum products yard. There were no injuries from the fire.

The base has been subject to almost daily mortar attacks, but this was the first time the attacks caused significant casualties and damage.

The attack came only days after the US occupation authorities handed over power to an interim Iraqi government. About 160,000 foreign troops - most of them Americans - remain in Iraq to provide security and train Iraq's new security services. 

Mortars were also fired late on Tuesday at a US base near Balad, 80km north of the capital, said Major Neal O'Brien. No casualties or damage were reported.

Brothers killed

Also, two Iraqi brothers were killed preparing a bomb at a home near Baquba, north of Baghdad, Iraqi police have said.

"The explosion happened Tuesday at 8:00 pm (16:00 GMT) at a home in Kahlis, 20km north of Baquba, killing one of the brothers and seriously injuring the other who died on the way to the hospital," said police officer Muhammad Jassim.

He said the brothers were preparing a home bomb, apparently for use in an attack.

Over the past week, Baquba, 60km north of Baghdad, has been the scene of attacks against police and the offices of political parties affiliated with the new caretaker government.

Dozens of people have been killed in the attacks.