BAGHDAD, March 14: Bomb attacks in Baghdad killed four US soldiers, the army said on Sunday, bringing to nine the number of troops killed in Iraq in the last four days by explosives planted by guerillas to target American patrols.

A military spokesman said a roadside bomb blast in southern Baghdad around 10.45pm on Saturday killed three US soldiers and wounded one. Another bomb attack at 8.30am on Sunday wounded an American soldier who later died in hospital, the spokesman said.

On Saturday, a bomb was detonated as a US patrol passed in Saddam Hussein's hometown of Tikrit. Guerillas then opened fire. Two soldiers were killed and several wounded.

Two bomb attacks on Wednesday and Thursday in the restive "Sunni triangle" around Baghdad killed three soldiers. Since the start of the war to oust Saddam, 389 US troops have been killed in action in Iraq.

Most of the deaths in recent months have been caused by roadside bombs, which the US army calls "improvised explosive devices". The low-tech bombs, often made from artillery shells crudely wired to a detonator, have taken a deadly toll.

The US military says most insurgents fighting occupying forces are still Iraqis, but that foreign militants are playing an increasing role in planning and executing major attacks.

Last Tuesday, two US civilians seconded from the Department of Defense and their Iraqi translator were shot dead in an ambush on a road south of Baghdad. They were the first American employees of the US-led civilian administration to be killed in Iraq.

A senior coalition official said the US Federal Bureau of Investigation had assigned a team to investigate the killings of the two, named as Fern Holland, 33, a lawyer, and Robert Zangas, 44, a press officer.

The US military said six people had been detained in connection with the incident and that four of them were believed to be legitimate members of the Iraqi police force. -Reuters