Saudi Arabia has responded angrily to allegations in a United States congressional report about its role in the 11 September attacks.
The FBI insists it could not have prevented the attacks
The 900-page report on the intelligence failings in the run up to the event accuses Riyadh of providing assistance to the hijackers and failing to co-operate with the US intelligence agencies.
Referring to the secret section of the report, the Saudi ambassador to the US, Prince Bandar bin Sultan, said "28 blanked-out pages are being used by some to malign our country and our people".
"Saudi Arabia has nothing to hide. We can deal with questions in
public, but we cannot respond to blank pages."
The White House has blocked publication of the section of the report dealing with the alleged Saudi involvement, so full details of the accusations are not known.
The Saudi Government has consistently denied any links with the hijackers.
BBC security correspondent Frank Gardner says the criticism of the Saudis among intelligence agencies has not been so much of what they did but what they did not do to combat extremists.
But he says a major crackdown has been happening since 12 May - when Saudi Arabia suffered suicide bombings that left 34 people dead.
In fact, our correspondent says, there is now a feeling among some Saudis that their leaders' response has gone too far.
The report says the 11 September attacks could have been prevented if the right combination of "skill, co-operation, creativity and good luck had been brought to bear".
However, it concludes that there was no one piece of intelligence that "would have identified the place, date or time of the attacks".
The report also criticises the Federal Bureau of Investigation (FBI) and the Central Intelligence Agency (CIA) for the breakdown in their communication.
Among the 16 recommendations, the document urges that a new system of accountability be put into place across the whole intelligence community in the US.
Some of the failings listed in the report are well known, such as the warning from an FBI agent about Middle Eastern men attending flight training schools that was ignored by FBI headquarters, says the BBC's Rob Watson in Washington.
But some of the information is new.
The report says that in May 2001 a key hijacker, Khalid Sheikh Mohammed, had been identified in an intelligence report as seeking recruits to travel to the United States for terrorist activities.
Those individuals would be expected to make contact with "colleagues" already there, it said.
The report also says two of the hijackers had had "numerous contacts" with an FBI informant in San Diego who was not aware that they were al-Qaeda militants.
The two, Nawaq Alhamzi and Khalid al-Mihdhar, had been identified as members of Osama Bin Laden's network after attending an al-Qaeda meeting in Malaysia in January 2000, the report says.
However this information was not passed on to the FBI, according to the congressmen.
The document says a student who provided al-Mihdhar and Alhazmi with financial help, Omar al-Bayoumi, "had access to seemingly unlimited funding from Saudi Arabia".
There have been calls by the chairman of the investigation, Senator Bob Graham, and others to declassify the sections of the report dealing with alleged Saudi links.
Hijacker Nawaq Alhamzi was known to the CIA
"President Bush needs to declassify parts of the congressional report that detail Saudi Government involvement in the events leading up to the 9/11 terrorist attacks," Representative Eliot Engel said.
However House Minority Leader Nancy Pelosi, a Democrat, defended the classification, saying it was "intended to protect sources and methods" rather than "reputations and countries".
"No one will ever know what might have happened had more connections been drawn between these disparate pieces of information," the report said.
Although the report was completed in December, it has taken until now for it to be declassified.
The congressional report follows hearings by the joint committee last year.
A separate independent commission is also looking into the 11 September attacks and is expected to make its conclusions next May.