A senior United Nations official has accused US-led coalition troops of depriving Iraqi civilians of food and water in breach of humanitarian law
Human rights investigator Jean Ziegler said they had driven people out of insurgent strongholds that were about to be attacked by cutting supplies.
Mr Ziegler, a Swiss-born sociologist, said such tactics were in breach of international law.
A US military spokesman in Baghdad denied the allegations.
"A drama is taking place in total silence in Iraq, where the coalition's occupying forces are using hunger and deprivation of water as a weapon of war against the civilian population," Mr Ziegler told a press conference in Geneva.
He said coalition forces were using "starvation of civilians as a method of warfare."
"This is a flagrant violation of international law," he added.
Mr Ziegler said he understood the "military rationale" when confronting insurgents who do not respect "any law of war".
But he insisted that civilians who could not leave besieged cities and towns for whatever reason should not suffer as a result of this strategy.
Lieutenant Colonel Steve Boylan, a US military spokesman, later rejected the accusations.
"Any allegations of us withholding basic needs from the Iraqi people are false," he said.
Even though some supplies had been delayed during fighting, he argued that "all precautions" were being taken to take care of civilians.
"It does not do relief supplies any good if you have them going into a firefight," he said.
The Geneva Conventions forbid depriving civilians of food and water.
Cutting off food supply lines and destroying food stocks is also forbidden.
Mr Ziegler, who opposed the US-led invasion of Iraq, said he would urge the UN General Assembly to condemn this practice when he presented his yearly report on 27 October.