United States President George W Bush for the first time on Wednesday defended British Prime Minister Tony Blair against allegations he exaggerated evidence of Iraq's alleged weapons programme.

"He (Blair) operated on very sound intelligence and those accusations are simply not true," Bush said in a brief show of support for his embattled Iraq war ally.

Until now, the American president has steered clear of the controversy engulfing Blair, and the two leaders have had few public contacts in recent weeks.

Both have been dogged by critics who allege they hyped the threat posed by Baghdad to build the case for war.

But Blair in particular faces mounting political pressure at home to produce evidence of banned Iraqi weapons that he said justified Britain joining the United States in military action.

US forces have not found chemical or biological weapons since ousting Iraqi President Saddam Hussein in April.

Bush has cited the discovery of suspected bio-labs as proof of progress in the weapons hunt, and White House officials say it will take time to uncover the extent of Iraq's illicit programmes.

"This has been a very careful search, and a search that has turned up things that we have previously talked about applying to the weapons of mass destruction program that the Iraqis had," White House spokesman Ari Fleischer said.

Bush has dismissed those questioning his justification for the invasion of Iraq as 'revisionist historians'.

US lawmakers on the House of Representatives Intelligence Committee planned on Wednesday to start a review of what intelligence agencies told Bush administration officials about the threat posed by Iraq before the war.

Compared to the months leading up to the war in Iraq, when Bush and Blair conferred almost daily, the White House has disclosed few calls between the two leaders since their April 8 meeting in Northern Ireland.

The White House largely kept quiet a bilateral meeting on the sidelines of the G8 summit in France earlier this month.

And tentative plans were scrapped for bilateral talks in England after Bush's landmark summit with Israeli and Palestinian leaders in Jordan.

Bash opted instead to shave a few hours off his homebound flight by taking a more direct route over Iraq.

Administration officials insist that Bush and Blair still talk regularly by phone but that many calls are not made public.