The report will criticise the Federal Bureau of Investigation (FBI) and the Central Intelligence Agency (CIA) but will conclude they had no evidence that gave specific warnings about the attacks, leaks to the American media suggest.

The 900-page report is expected to provide details of missed opportunities to disrupt the terror plot by denying entry to the hijackers and keeping them under surveillance.

The report was completed in December, but it has taken until now for it to be declassified.

But it reportedly leaves unanswered questions about whether Saudi Arabia funded or had any knowledge of the al-Qaeda hijackers, 15 of whom were Saudi nationals.

The Bush administration has refused to declassify 28 pages of the report that deals with the actions of the Saudis and other foreign governments.

Senator Bob Graham, one of the leaders of the joint House and Senate investigation, and a Democrat who wants to challenge President George W Bush for the White House next year, has accused the administration of protecting foreign governments.