I personally think that this issue now has become far more prominent, far more consequential and needs to be investigated and clearly considered in a far more comprehensive way

Tom Daschle Senate Majority leader

House of Representatives Democratic (Minority) leader Richard Gephardt told CNN it was necessary to find out what President Bush and his staff knew and when they knew it.

His Democrat counterpart in the Senate, Majority leader Tom Daschle, on Thursday urged Mr Bush to hand over all the information he had received to Congress.

The renewed calls come after the revelation that the president was informed in August that the al-Qaeda terrorist network might be planning to hijack aircraft.

There were further revelations on Friday - White House spokesman Ari Fleischer said security officials had prepared an order to dismantle Osama Bin Laden's al-Qaeda network just before 11 September - but, because of the attacks, Mr Bush never saw them.

You would have risked shutting down the American civil aviation system with such generalised information

Condoleezza Rice

In a White House briefing on Thursday, US National Security Adviser Condoleezza Rice said the information passed to President George W Bush was very generalised and did not relate to the possibility of attacks on buildings.

But the disclosure of the 6 August briefing has sparked the biggest row in Congress since the attacks, with many Democrats criticising the government for the first time over its War on Terror.

Citizens' commission

US Vice-President Dick Cheney hit back at the administration's critics, saying that some of their comments had been "thoroughly irresponsible and totally unworthy of national leaders in a time of war".

About 3,000 people died in the 11 September attacks

The BBC's Alex Van Wel says that while there is undoubtedly a whiff of politics in the air, Mr Bush will nonetheless have to address the accusations squarely before long.

Democrat Senator Jo Lieberman and Republican John McCain have been pushing for legislation to create a citizen's commission for some time, but are now demanding an inquiry.

"It is irresponsible to point fingers and lay blame without all the facts, but it is equally irresponsible to allow this type of information to trickle out slowly and haphazardly, raising new questions, tearing at old wounds, and alarming the public," Senator Lieberman said on Thursday.

But some legislators are opposed to any new inquiry, on the grounds that investigations by the two houses' intelligence committees are already under way.

House intelligence committee chairman Porter Goss said his inquiry had found "no smoking gun" and no further probes were necessary.

The joint investigation is due to begin hearings next month.

'No specific warning

At Thursday's briefing, Ms Rice told reporters the main concern of the administration before 11 September was over possible attacks on American interests overseas.

Cheney: Investigation should not interfere with efforts to prevent attacks

"I don't think that anybody could have predicted that these people would take an aeroplane and slam it into the World Trade Center, take another one and slam it into the Pentagon," she said.

Ms Rice revealed that counter-terrorism officials met almost daily in the summer of 2001 to evaluate the threats.

She said US airlines had been specifically warned in August that terrorist groups were developing ways of carrying out hijackings, using disguised weapons such as mobile phones and key chains.

But there was no specific warning, she insisted, and to make public such threats might have meant closing down the country's entire aviation industry.

Ms Rice denied there had been an intelligence lapse, saying the US had successfully foiled attacks on Rome, Turkey and Paris as a result of its intelligence efforts.