The soldier belonged to the 352nd Civil Affair Command -- a non-combat unit -- which had been involved primarily in the reconstruction of post-war Iraq, assessing which public works projects have priority and assigning funds to them, a spokeswoman said.

His convoy was hit by an "improvised explosive device" on a Baghdad highway.

The death raises to at least 23 the number of Americans killed by hostile fire in Iraq since President Bush declared major combat over on May 1.

The United States and Britain have insisted they will not pull out of Iraq, despite ongoing attacks on their troops.

President George W Bush made the pledge on Tuesday when six American soldiers were wounded in two separate attacks in the Iraqi capital, Baghdad.

And UK Foreign Secretary Jack Straw said the incidents had increased London's and Washington's determination to root out remnants of Saddam Hussein's regime.

Mr Straw is visiting the southern city of Basra - a day after a memorial service for six British soldiers killed last month.

More than 20 US soldiers have died as a result of hostile fire since 1 May when President Bush declared major operations in Iraq over.

BBC Washington correspondent Justin Webb said senior politicians of both main parties in Washington have been pressing the White House to be clearer about the nature of the commitment the US is going to have to make if Iraq is to be put on the road towards democracy.

At a military swearing-in ceremony, Mr Bush talked of the massive and long-term undertaking that would be necessary.

Visiting the southern city of Basra, which is under UK military control, the British foreign secretary said the Americans had a more difficult area to control around Baghdad.

The capital was the centre of Saddam's regime and is now the apparent focus for remnants of his Baathist party.

Mr Straw said the search for further evidence of Iraq's weapons of mass destruction - the main reason for going to war - would go on.

The chief US administrator in Iraq, Paul Bremer, has dismissed recent attacks as the predictable and increasingly desperate response of the ousted regime.

Although they appeared co-ordinated locally, there was no evidence the attacks were part of a centrally-controlled campaign, he said.

Suggestions that troops are facing an organised insurgency have been dismissed by US Defence Secretary Donald Rumsfeld, who insisted they were not becoming bogged down in a Vietnam-style guerrilla war.