Meanwhile, a British battle group headed to deadlier zones near the capital despite pleas from a British hostage to abort the mission, requested by the United States to help restore order ahead of elections.

And Japanese officials were racing against the clock to secure the release of a young Japanese man kidnapped by Islamic militants, with less than 24 hours to go before a deadline for his execution.

Highlighting the risks of operating around Baghdad, the early morning bomb exploded in the path of a US military patrol under a flyover.

Three US soldiers were wounded, with one later dying, while one and possibly two Iraqi civilians were also killed, the US military said.

An ordanance team was trying to establish whether the explosion was of a car bomb or a roadside bomb, it added.

Witness saw flames spewing from a US army vehicle after the attack at about 7:30 am (0430 GMT).

"The impact was so strong I was blown away," said Mohammed Jassem, 42, who had been trying to fix his car at the time just metres (yards) away.

Jassem said he had been trying to drive to the restive town of Mahmudiyah, which lies between Baghdad and Hilla in the violent-wracked province of Babil, where the 850-strong British battle group is said to be headed.

A British military spokesman declined Thursday to give further details of the controversial mission, a day after scores of tanks, Land Rovers and other vehicles, packed with soldiers from the Black Watch battalion, left their base in Iraq's relatively calm city of Basra in the south.

Britain agreed last week to a US request to move 850 crack troops to Babil province as US soldiers focus on wresting Fallujah from rebel control.

The redeployment marks the first time since the March 2003 invasion of Iraq that British troops have left southern Iraq for US-controlled areas, where they are considered more likely to come under hostile fire.

Upping the stakes, kidnapped Briton Margaret Hassan begged anew for the withdrawal of British troops from Iraq and the release of Iraqi women prisoners.

Hassan, a British-Iraqi national taken hostage last week, "issued an appeal to Britons to urge British Prime Minister Tony Blair to withdraw his troops from Iraq and not redeploy them in Baghdad", Al-Jazeera television said Wednesday.

In a separate drama, there was no fresh news on the fate of 24-year-old Shosei Koda of Japan, who had reportedly gone to Baghdad as a tourist and searched aimlessly for a hotel before being kidnapped by a group linked to Iraq's most wanted man, Abu Mussab al-Zarqawi.

The group has threatened to behead Koda within 24 hours unless Japan pulls out some 600 troops from Iraq -- a demand Tokyo has rejected.

Chief Cabinet Secretary Hiroyuki Hosoda, the top government spokesman, said Japan had asked for "the cooperation of 25 countries including Iraq, the United States and Britain."

Baghdad and top allies Washington and London are determined to restore order to Iraq in time for national elections planned for January -- by force if necessary.

To this end, US warplanes again bombed the restive city of Fallujah, west of the capital, in the hunt Zarqawi and his followers who are believed to use the Sunni Muslim bastion as an operating base.

"Several credible intelligence sources confirmed that members of the terrorist group were at this location to plan attacks on innocent civilians and Iraqi security forces," a military statement said.

Doctor Ahmed Khalil at the city's main hospital said three people died in the raid, while witnesses said the house had been hit in previous air strikes.

The US military always insists that its strikes in Fallujah are "precise" and with minimum collateral damage, while hospitals report civilian casualties.

Since October 14, US troops have encircled Fallujah, where the military has repeatedly launched air strikes and some limited ground incursions.

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