The terrorist attack foiled by British authorities was aimed at blowing up as many as 10 planes on transatlantic flights, with a dry run planned within two days, according to US intelligence officials.
The actual attack would have followed within days.
One official said the suicide attackers planned to use a peroxide-based solution that could ignite when sparked by a camera flash or another electronic device.
The test run was designed to see whether the plotters would be able to smuggle the needed materials aboard the planes, these officials said.
They spoke anonymously because of the sensitivity of the subject matter.
The test run was designed to see whether the plotters would be able to smuggle the needed materials aboard the planes, the officials said.
The details of the alleged plot surfaced as the administration posted a maximum code-red alert for passenger flights from England to the US and banned liquids from all carry-on bags.
The security upgrade triggered long lines at airports across the US, and governors in at least two states activated National Guard troops to help provide protection.
"This was a well-advanced plan," homeland security secretary Michael Chertoff said as British authorities announced the arrests of 24 alleged plotters yesterday. "In some respects suggestive of an al Qaida plot."
Los Angeles mayor Antonio Villaraigosa said as many as 10 flights had been targeted.
Other officials said they were United, American and Continental Airlines routes from Britain to the major US summer tourist destinations of New York, California and Washington DC.
Virginia's deputy homeland security director, Steven Mondul, said that in a morning conference call, federal officials pointed to New York's John F Kennedy Airport, Los Angeles International and Dulles Airport outside Washington as "major destinations for flights originating from the United Kingdom". No specific warnings were issued for these facilities, he added.
White House spokesman Tony Snow said President George Bush had been briefed in advance of the events and had approved raising the alert to red on flights from England.
In brief remarks from Wisconsin, the president said the events showed the nation "is at war with Islamic fascists".