The Geneva Conventions on warfare, which form the basis of international humanitarian law, not only forbid denying food to civilians, but actually make the occupying force responsible to provide it, he said. "This is a flagrant violation of international law."
A US military spokesman in Baghdad, Lt-Col Steve Boylan, dismissed the criticism as inaccurate. "Any accusations of coalition forces refusing basic needs from the citizens of Iraq are completely false," he said.
Mr Ziegler said he would present a report on 27 October at the UN General Assembly in New York expressing his personal "outrage" at the alleged practice and calling on countries to condemn it in a resolution. He cannot submit a UN resolution himself.
The UN's food expert presents an oral report each autumn at the UN General Assembly and a written report each spring at the 53-nation UN Human Rights Commission.
"I can understand the military rationale, facing such a horrible enemy, this insurgent, who does not respect any law of war," Mr Ziegler told reporters.
He conceded that the practice helped to "save tens of thousands of lives" but made the point that many civilians were unable to come out.
Those that remained behind in insurgent strongholds such as Fallujah, Tal Afar and Samarra have suffered as a result of broken supply lines, he asserted.
And some have even starved, he claimed.