The US delegation has walked out of the United Nations as Iraq condemns US aggression.
Negroponte had finally run out of patience with Iraq's "preposterous allegations"
John Negroponte, the US ambassador, left the Security Council chamber while Mohammed al-Douri, his Iraqi counterpart, was winding up his speech condemning US aggression against Iraq.
"I did sit through quite a long part of what he had to say, but I had heard enough after what he had to say and did not hear anything new," Mr Negroponte said.
He said he was fed up with hearing preposterous allegations against the US.
Iraq's UN envoy charged that the United States and its allies were beginning a "war of extermination" against the Iraqi people, and had arranged for contracts to rebuild Iraq in 1997, six years before the war began.
The move came at a delicate time at the UN, as negotiations are under way on its future role in administering aid to Iraq.
I had heard enough
US Ambassador John Negroponte
UK Prime Minister Tony Blair was en route from Washington to meet UN Secretary General Kofi Annan in New York, following his summit with US President George W Bush at Camp David.
The two leaders agreed that the key to humanitarian relief in Iraq was progress in the war, a point echoed by Mr Negroponte.
Mr Blair said that it was urgent to clarify the role of the UN in administering humanitarian relief in Iraq.
The US and Britain are preparing to bring in relief supplies as soon as possible.
Mr Annan emphasises that under the Geneva Conventions, the powers exercising authority on the ground - that is, in many areas, the Americans and British - are primarily responsible for the well-being of the population.
But the US and UK want to reactivate the UN oil-for-food programme, which has fed 60% of Iraqis for several years.
The programme has the resources for a large-scale operation, but it was suspended when the UN pulled its expatriate staff out of Iraq when the war began.
Ambassador Negroponte had been urging the UN to approve a new resolution to restart the programme.
Diplomats say some members of the council - notably Syria but also France, Russia and China - are reluctant to approve wording that that would indirectly legitimise the military action.
Mr Negroponte defended the US-led coalition, says that its action in Iraq was "legitimate and not unilateral" as well as an "appropriate response."
These same arguments are at the heart of the controversy over what the long-term role of the UN should be.
Beyond humanitarian aid, Mr Annan says further UN involvement will have to be decided by the member states through another, more far-reaching Security Council resolution.
Tony Blair has been urging President Bush to ensure that the UN plays a substantial role in governing Iraq in the transition phase.
And he has been supported by US Secretary of State Colin Powell, who said on Wednesday that he saw a role for a UN coordinator in a post-war Iraq.
But some in the US administration would prefer to steer clear of the UN in the long term, arguing its role has been undermined by its failure to agree a second resolution against Iraq.