The White House Thursday struggled to defend the dire warnings about Iran made by US President George W. Bush even after he had learned that Tehran had likely frozen its atomic weapons program in 2003.

A new US National Intelligence Estimate (NIE) released on Monday formally endorsed that conclusion, which Bush had first heard about in August from US Director of National Intelligence Michael McConnell.

On August 28, Bush warned of a "nuclear holocaust" if the Islamic republic developed nuclear weapons, and on October 17 he warned that anyone interested in avoiding "World War III" should support US pressure on Tehran.

On Tuesday, the US president defended himself from Democratic charges of exaggerating the threat by saying that he had only been briefed on the NIE on November 28 and suggesting that McConnell's warning had been vague.

"In August, I think it was, Mike McConnell came in and said, 'we have some new information'. He didn't tell me what the information was. He did tell me it was going to take a while to analyze," Bush told a press conference.

But White House spokeswoman Dana Perino said one day later that McConnell had told Bush that he was looking into new information casting doubt on previous US charges that Iran sought nuclear weapons.

McConnell "said that if the new information turns out to be true, what we thought we knew for sure is right. Iran does in fact have a covert nuclear weapons program, but it may be suspended," she said.

Confronted with the apparent contradiction between her comments and Bush's own words, Perino replied: "The president could have been more precise in that language. But the president was being truthful."