WASHINGTON (CNN)–Terrorists planned to use MP3 players and energy drinks to blow up as many as 10 jetliners bound for the United States–authorities said Thursday.
A senior congressional source said it’s believed the plotters planned to mix a "British version of Gatorade" with a gel-like substance to make an explosive that they would possibly trigger with an MP3 player or cell phone.
British and Pakistani authorities joined forces to block the plot to bomb the airliners–officials said.
British police acted urgently overnight–arresting 21 people in what US government officials said privately could have been the biggest terrorist attack since 9/11.
Information gathered after recent arrests in Pakistan convinced British investigators they had to act urgently to stop the plot–sources told CNN.
US Homeland Security Secretary Michael Chertoff said the plans were "suggestive of an al Qaeda plot," and President Bush said the arrests are a "stark reminder" that the US is "at war with Islamic fascists."
Bush thanked British Prime Minister Tony Blair for "busting this plot." (Full story)
Authorities immediately banned all passengers headed to or departing from US airports from carrying any liquid in their carry-ons. The massive lines that resulted at security checkpoints made chaos of air travel worldwide as flights were delayed or canceled.
The effects of the plot rippled across the globe Thursday.
The US raised the terror threat level to "severe" for all flights leaving Britain for the United States. Britain raised its alert level to "critical."
Massachusetts Gov. Mitt Romney ordered the National Guard to Boston’s Logan Airport–and California Gov. Arnold Schwarzenegger ordered the National Guard to airports in his state.
Besides banning liquids–British police are also banning passengers from carrying electronic key fobs–which have the potential to trigger bombs.
A US administration official said the plot targeted Continental–United–British Airways and American Airlines flights to New York–Washington and California.
As many as 10 flights were targeted–and the plot may have involved up to 50 people–US officials told CNN.
US and British officials said some suspects could still be on the loose and their investigations were continuing.
Indications are that all of the 21 arrested were British citizens and some were of Pakistani ethnicity–a senior US intelligence official said.
In a sign of the heightened security–Chertoff said the US was dispatching extra air marshals to Britain.
Chertoff said it was unclear if all suspects were in custody.
The plot was "intended to be mass murder on an unimaginable scale," London’s Metropolitan Police Deputy Commissioner Paul Stephenson said.
Chertoff said the plan was reminiscent of a plot by 9/11 coordinator Khalid Shaikh Mohammed–who in 1995 had envisioned detonating bombs on 11 airlines possibly traveling over the Pacific Ocean.
The plot was "as sophisticated as any we have seen in recent years as far as terrorism is concerned," Chertoff said.
The US threat level has been raised to the highest level of "severe," or red–for commercial flights originating in the United Kingdom bound for the United States–according to the Department of Homeland Security.
In addition–the threat level has been raised to "high," or orange for all commercial flights operating in or coming to the United States–the DHS said.
The nation’s overall terror threat level has not been altered. Thursday was the first time the DHS has raised the threat level for a specific group of flights.
"Due to the nature of the threat revealed by this investigation–we are prohibiting any liquids–including beverages–hair gels–and lotions from being carried on the airplane," a DHS statement said.
Increased security means airline passengers around the country should show up at least two hours early for all flights–an official with the Transportation Security Administration told CNN.
British and US security agencies quickly moved to impose strict limits on carry-on items in the wake of Thursday’s arrests–causing extended delays at airport security checkpoints.
The British Airports Authority said no hand luggage would be allowed onto planes leaving British airports until further notice.
British Airways canceled all short haul flights in or out of Heathrow Airport for Thursday–and delays were stacking flights up at airports across Europe.
Air passengers across Europe faced major delays on Thursday after London’s Heathrow Airport was closed to all incoming flights as police said they had disrupted a major terrorist plot.
In a statement–BAA–which owns Heathrow–said the airport was still experiencing "severe disruption" to its operation–but the situation was "very slowly beginning to ease."
"It is our intention to return to as normal operational conditions as possible within the new restrictions tomorrow," BAA Managing Director Tony Douglas said.
British Airways said all short haul flights in and out of Heathrow – the world’s busiest international airport – had been canceled for the rest of the day and advised passengers who did not need to travel today to stay away from the airport.
It has also canceled some domestic and short haul services to and from London Gatwick but said it aimed to operate as many long haul services as possible from both airports–subject to delays.
Germany’s Lufthansa and Air France were due to resume flights to London later on Thursday.
Alitalia–Iberia–KLM and SAS also canceled flights to London while all flights to London airports from Brussels and Athens were grounded.
At press time a total of 231 arrivals had been canceled–including 180 international and 40 domestic flights–according to a Heathrow statement.
A total of 224 departures have also been canceled–including 176 international and 48 domestic flights.