"Based on my experience with the (Bush) administration in the months leading up to the war, I have little choice but to conclude that some of the intelligence related to Iraq's nuclear weapons program was twisted to exaggerate the Iraqi threat," Joseph Wilson wrote in a New York Times opinion piece on Sunday.

US government officials repeatedly claimed that Iraq possessed banned chemical, biological and nuclear weapons as they sought UN approval to invade Iraq on the grounds that the Gulf nation posed an immediate threat to the United States.

US President George W. Bush said during his State of the Union address that Iraq had purchased processed uranium in Africa. Britain repeated the claim. Wilson doubted both.

"My judgment on this is that if they were referring to Niger when they were referring to uranium sales from Africa to Iraq, that information was erroneous and that they knew about it well ahead of both the publication of the British white paper and the president's State of the Union address," he said on NBC's "Meet the Press."

The Central Intelligence Agency sent Wilson to Niger to check the charge on behalf of Vice President Dick Cheney. He was a diplomat 1976-1998 with a broad knowledge of Africa.

The CIA asked Wilson to answer questions from Cheney about an intelligence report citing a memorandum of agreement between the two countries documenting the possible sale.

Although Wilson had not seen the document himself, he said news reports showed that it was an obvious forgery, having the signatures of government officials who were not in office on the date that appears on the document.

Wilson said he spent eight days talking to dozens of people in Niger, and wrote in the Times that it was "highly doubtful" that any such transaction took place.

Niger's two uranium mines are run by French, Spanish, Japanese, German and Nigerian interests. If the Nigerian government wanted to remove uranium from a mine, "it would have to notify the consortium, which in turn is strictly monitored by the International Atomic Energy Agency," he wrote.

"In short, there's simply too much oversight over too small an industry for a sale to have transpired," he added.

Wilson was surprised when, in December, the State Department published a fact sheet mentioning the Niger sale, and in January, Bush repeated the charges that Iraq tried to buy uranium from Africa.

"If my information was deemed inaccurate, I understand (though I would be very interested to know why). If, however, the information was ignored because it did not fit certain preconceptions about Iraq, then a legitimate argument can be made that we went to war under false pretenses," Wilson wrote.

Several questions remain, Wilson told NBC.

"Had we decided upon going to war and were we using the grave-and-gathering-danger argument -- the imminent threat to our national security posed by Saddam's weapons of mass destruction programs -- as justification for a war that we had already decided to go to?"

"That is a trivialization of the weapons of mass destruction problem," he said.

For Wilson, there is "no greater threat" that the United States faces "than the threat of weapons of mass destruction in the hands of nonstate actors or international terrorists."

However if the Bush administration used the issue of WMDs as cover to go to war for other reasons, "then I think we've done a grave disservice to the weapons of mass destruction threat," he said.

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