US President George W Bush has given details of what he said was a foiled al-Qaeda plot to fly a plane into the tallest building on the US west coast.
Mr Bush said the plan - uncovered in 2002 - involved using shoe bombs to blow open the plane's cockpit door.
The intended target was the 73-storey Library Tower in Los Angeles, renamed the US Bank Tower.
Mr Bush said al-Qaeda had recruited the militant Islamic group Jemaah Islamiah (JI) to carry out the attack.
The president said the alleged mastermind of the 11 September 2001 attacks, Khalid Sheikh Mohammed, was behind the west coast plot.
Mr Bush said that instead of using hijackers of Arab origin, as in the attacks on New York and Washington, Sheikh Mohammed recruited "young men from South East Asia whom he believed would not arouse as much suspicion".
Planning began in October 2001, but it was derailed in early 2002 "when a South East Asian nation arrested a key al-Qaeda operative", Mr Bush said.
The plot was finally thwarted in the summer of 2003, when a man suspected to be a key member of JI, an Indonesian known as Hambali, was arrested in Thailand.
The Bush administration first mentioned the alleged plot last October, without giving details, saying it was among 10 disrupted al-Qaeda plans.
The president revealed the newly declassified details in a speech on Thursday at the National Guard Memorial Building in Washington.
He said the US-led war on terror had "weakened and fractured" al-Qaeda and other groups but warned they were "still lethal".
The BBC's Justin Webb in Washington says that while Mr Bush plainly meant to warn Americans of the continuing danger posed by international terrorism, the only really new detail was that of the shoe bombs.
It comes as the White House is under pressure from some of the president's own supporters to be more aggressive in talking up the successes of intelligence gathering, our correspondent says.
US BANK TOWER, LA
Height: 310m (1,018ft)
Tallest building in US, west of Chicago
Formerly called Library Tower
"Crown" lights up at night
Was "blown up" in Independence Day film
The administration needs to persuade Americans that measures such as the highly controversial tapping of phones without court warrants are fully justified.
Officials would not say whether these domestic US phone taps contributed to information gained about the Los Angeles plot, our correspondent says - but they left open at least the possibility that they did.
Briefing reporters after the speech, White House counter-terrorism adviser Frances Fragos Townsend added further details to Mr Bush's revelations.
All four members of the terror cell had been arrested, she said, but refused to disclose where they were being detained.
She added that two South Asian countries and two from South East Asia had helped derail the plot, but did not identify them.
'Bush the protector'
In Los Angeles, Mayor Antonio Villaraigosa told the Associated Press news agency he had not been forewarned about the president's revelations.
"I'm amazed that the president would make this [announcement] on national TV and not inform us of these details through the appropriate channels," he said.
Democratic congressman Brad Sherman told the BBC that he had concerns about why the information was being released now.
He questioned whether the president's obligation to "manage secrecy" had been over-ridden by his "natural desire to create a vivid picture of 'Bush the protector' for political reasons".