The complex attack Thursday began with a roadside bomb, the military said in a statement. Small arms fire and rocket-propelled grenades followed shortly after the blast, it said.

All seven wounded soldiers were evacuated to a military hospital, and one has since returned to duty, the military said.

The victims' names were withheld pending family notification.

The deaths brought to 99 the number of US troops who have died in Iraq this month. Last month, at least 126 US military personnel died, making May the deadliest month for US forces in Iraq since November 2004.

At least 3,576 members of the US military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count. The figure includes seven military civilians. At least 2,936 died as a result of hostile action, according to the military's numbers.

Earlier US forces killed three people they described as militants and detained more than two dozen in a series of raids across Iraq on Friday targeting al-Qaeda networks.

The military said troops killed the three militants, one of whom was wearing a suicide vest, in a raid near the former rebel town of Fallujah in the western Sunni Anbar province.

In the same raid troops detained 16 militants for their alleged ties to a "top al-Qaeda in Iraq leader", while in the same province near the town of Karmah, another raid led to arrest of four more militants, the military said.

In a third operation south of Baghdad, troops searched a building to arrest a close aide of a militant known for orchestrating vehicle bombings in the capital, capturing the suspect and two other militants.

A fourth raid resulted in the arrest of another aide of a leader of al-Qaeda in the region of Tarmiyah, near Baghdad, the military said.

And in Mosul, two more suspects were detained in a raid targeting a top leader of al-Qaeda operating in the disputed oil-rich city of Kirkuk in northern Iraq.

"We're continuing to target the top of the terrorist network, as well as the operatives who carry out their murderous actions," said Lieutenant Colonel Christopher Garver of the US military in the statement.

In other developments, Iraqi police said a bomb exploded under an oil pipeline south of Baghdad on Friday, spilling crude oil and sparking a huge fire.

The explosives were planted under a stretch of pipeline in the Mowehlah area of Haswa, a town 50km south of the Iraqi capital, a police officer said on condition of anonymity because he was not authorised to release the information.

The pipeline transmits crude oil from Iraq's southern oil fields to the Dora refinery in Baghdad.

The blast ignited a huge fire around 5 am, the officer said. By midday, firefighters were still struggling to extinguish the flames, which were fuelled by a continuing leak of oil from the pipeline, he said. Workers also were looking for a way to temporarily cut off the oil flow, until a repair could be made, the officer added.