Leading congressmen in the United States are strengthening calls for a full independent inquiry into intelligence failures in the run-up to the 11 September suicide attacks.

Democrat Joe Lieberman and Republican John McCain are the latest senior voices to demand the setting up of an special commission.

The congressional panel which has been set up to investigate the work of US intelligence agencies has had its inquiries disrupted by disputes between the panel and intelligence agencies, according to reports in the Washington Post.

The question really is... was (President Bush) given enough information?

Senator Joe Lieberman

And the Federal Aviation Authority (FAA) has come under fire for failing to act on the news that terrorist suspect Zacarias Moussaoui had been arrested shortly before the 11 September attacks in which investigators believe he planned to take part.

According to reports in the Wall Street Journal, the FAA decided not to warn airlines to increase security, because the information was not specific enough.

The Federal Bureau of Investigation (FBI) reported that Mr Moussaoui had been detained after trying to learn how to pilot a Boeing 747, despite having almost no flying experience.

Details of the FAA's decision not to alert airlines have not been made public.

Al-Qaeda, the organisation headed by Osama Bin Laden, is believed to have organised the suicide attacks on 11 September, which killed about 3,000 people in New York, Washington, and Pennsylvania.

Question of information

President George W Bush is now likely to come under fresh pressure to reveal more about what was known about potential attacks prior to 11 September.

Joe Lieberman is calling for a new inquiry

But his Vice-President Dick Cheney has opposed the setting up of the public commission of inquiry, saying that energies should be concentrated on preventing future attacks.

Mr Lieberman stressed that he was not attacking the president himself.

"No one in his or her right mind thinks that President Bush was given specific warning of what might happen on September 11 and turned away from it," he said.

"The question really is... was he given enough information?"

Democrat Dick Gephardt believes that a team of independent experts, congressmen and Administration officials would be more effective that the current commission.

"I never ever, ever thought that anybody, including the president, did anything up to September 11 than their best. The question is, how do we do better?" he said.

Intelligence key

Mr Cheney has defended the Bush administration's handling of reports on al-Qaeda activity prior to the attacks, while acknowledging that intelligence agencies had failed to pool their information.

About 3,000 people died in the 11 September attacks

The extent of the concerns forced President Bush himself to speak out last Friday, saying he would have done everything in his power to stop the attacks if he had known in advance.

Congressmen are particularly keen to analyse details of a briefing Mr Bush received on 6 August about the risk of al-Qaeda hijackings.

But Mr Cheney said he would oppose the release of such material, because it could compromise future security operations.

"The thing we need more than anything else to defeat terror is intelligence," said Mr Cheney.

The existing congressional panel is made up of members of the House and Senate intelligence committees, and has a budget of $2.6m.

But some staff see deliberate delaying tactics behind delays in providing access to documents at the FBI and the US Justice Department, the Washington Post reported.

The opening hearing date of the panel has been delayed three times.