Three US soldiers and two Iraqis have been killed in a bomb attack on a patrol north of the capital Baghdad, the US military says.
Iraqis celebrated at the scene of the attack
It took the number of American troops killed since the war began in Iraq in March last year to 500.
Two soldiers were also injured when the roadside bomb exploded at Taji, about 30 km (20 miles) from Baghdad.
It is the latest in a series of deadly attacks on coalition forces which the US blames on the Iraqi resistance.
Meanwhile as debate continues over the issue of how Iraq should be run in future, the US says it intends to ask the United Nations to back its plans for the transfer of power.
The US administrator Paul Bremer is to meet UN Secretary-General Kofi Annan on Monday in a drive to get the UN to return to Iraq.
He is also expected to seek UN help in convincing the Shia majority that US proposals for an unelected transitional government are the best way to meet a July deadline for a handover of sovereignty.
On the ground, an advance team of Japanese soldiers is in neighbouring Kuwait preparing to join forces from other countries in helping Iraq's reconstruction efforts.
The US servicemen killed were taking part in a joint patrol with Iraqi civil defence staff looking for explosive devices.
Troops reportedly seized bomb materials and made arrests
Initial reports of the incident said the military vehicle was flipped over by the blast and caught fire.
"The improvised explosive device detonated by the front Bradley [fighting vehicle]
in the patrol, causing the vehicle to catch fire," Lieutenant Colonel William Macdonald of the 4th Infantry
Three Iraqis found to have bomb-making material in their vehicle were arrested in the area shortly after the blast.
Regular attacks against the occupation forces continue, many of them roadside bombs.
The latest deaths inside the "Sunni triangle" - which has seen the fiercest resistance to US-led forces - takes the total of US soldiers killed in Iraq since the war began to 500.
However US military officials say attacks are down to 15 a day from a high of 40 a day in November.
They say the security situation has improved enough to move most of their forces to the outskirts of Baghdad and turn over more responsibility to Iraqi policemen.
This is supposed to happen shortly when the army division in control of the city is replaced by new forces, says the BBC's Barbara Plett in Baghdad.