"First, he has not been to Iraq, and second, he is wrong," Kevin Moley, US ambassador to UN organisations in Geneva and a member of the American delegation to the 53-nation UN Human Rights Commission, said on Thursday.
"He's taking some information that is in itself difficult to validate and juxtaposing his own views - which are widely known," Moley said, referring to Jean Ziegler's opposition of the US military intervention in the country.
Ziegler, the commission's expert on the right to food, cited US and European studies on Wednesday in telling the commission that acute malnutrition rates among Iraqi children under five rose late last year to 7.7% from 4% after Saddam Hussein's ousting in April 2003.
Moley rejected the rate that he said was purported to be accurate by Ziegler. Moley said malnutrition in Iraq was notoriously difficult to gauge.
He noted that some estimates had put it at 11% in 1996 and 7.8% in 2000, while Hussein was still in power.
"The surveys that have been taken ... have indicated that the recent rise in malnutrition rates began between 2002 and 2003 under the regime of Saddam Hussein," Moley said.
"If anything, vaccination, food aid ... has improved dramatically since the fall of Saddam Hussein," he added.