WASHINGTON, Aug. 10 (Xinhua) -- A close-to-execution terror plot targeting flights from Britain to the United States which was intended to kill hundreds, has put the United States on its highest alert ahead of the 5th anniversary of the Sept. 11 attacks.

    Both U.S. and British officials confirmed Thursday that at least 21 suspects in London were in their final stage of plotting to blow up several U.S.-bound flights from Britain with liquid explosives they planned to take onboard. 
    

Two Metropolitan Washington Airport Authority employees assist a departing passenger discard personal items qualifying as "liquids and gels" which are no longer permitted at the Washington Dulles International Airport in Dulles, Virginia, August 10, 2006. (Xinhua/Reuters Photo) Photo Gallery >>>

    The latest news reports said the plot targeted at least three major U.S. carriers on flights from Britain, with destinations including at least five major U.S. cities.

    Alert levels were raised to their maximum at U.S. and British airports and air travel across Europe and in the United States faced mass disruptions.

    Earlier in the day, the Bush administration raised the threat level for flights from Britain to "red," designating a severe risk of terrorist attacks.

    It is the first time the red alert level in the Homeland Security warning system has been invoked.

    All other flights, including all domestic flights in the United States, were put under an "orange," alert, one step below the highest level.

    The administration also banned all liquids and gels from flights, including toothpaste, makeup, and suntan lotion, but baby formula and medicines were exempted.

    Airports across the United States beefed up their security on Thursday and some flights were canceled or delayed.

    Britain's threat warning level has been raised to "critical" --meaning an attack is expected imminently.     

    SECURITY BEEFED UP

    Responding to the elevated alert level, airports across the United States beefed up their security. 
    

A passenger empties her water bottle at a security checkpoint at Logan International Airport in Boston, Massachusetts August 10, 2006.(Xinhua/Reuters Photo) Photo Gallery >>>

    At Dulles International Airport near Washington DC, warning signs were put up to alert passengers in all-red capital letters, prohibiting liquids or gels from being taken onboard.

    Passengers dumped their liquids into large trash cans, with the result that they were filled so quickly that they had to be emptied every few minutes.

    At Dallas-Fort Worth International Airport in Texas, extra police and dog units were sent out overnight to patrol terminals and parking garages.

    In Chicago, aviation commissioner Nuria Fernandez said the only exceptions to the ban on liquids would be breast milk and fruit juices for small and nursing children.

    At Hartsfield-Jackson Atlanta International Airport in Georgia, some passengers were surprised by the sudden ban on flying with liquids.

    At most of the airports, prolonged security checks produced long queues of passengers.

    Media reports said the London plot had targeted United Airlines, American Airlines and Continental Airlines Inc. U.S. air carriers have canceled some flights due to the security concerns.

    American Airlines canceled three London-bound morning flights and three afternoon or evening flights from London to the United States.

    U.S. Customs and Border Protection agents will also step up security measures in international arrival areas, including the increased use of explosives detection technology, canine units and special response teams.

    The U.S. Transportation Security Administration will implement a series of additional security measures, including sending U.S. Federal Air Marshals to Britain to provide expanded coverage on flights between the two countries.

    "SUGGESTIVE OF AN AL QAIDA PLOT"

    U.S. Homeland Security Secretary Michael Chertoff told a morning press conference that the terror scheme was "suggestive of an al Qaida plot."

    He said the plot involved hiding masked liquid explosives and detonators in carry-on luggage. 
    

(Xinhua/Reuters Photo) Photo Gallery >>>

    Chertoff said the plan was reminiscent of a plot by 9/11 coordinator Khalid Shaikh Mohammed, who in 1999 had envisioned detonating bombs on 11 airliners 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," he said.

    Chertoff said the plotters were in the final stages of planning before execution, though it was unclear whether the plot was linked to the upcoming fifth anniversary of the September 11 terror attacks.

    U.S. Attorney General Alberto Gonzales said the operation "could potentially kill hundreds".

    FBI Director Robert Mueller also said the plot bears "the earmarks of an al Qaida plot."

    "We do believe the plot involved flights from the UK to the U.S. and was a direct threat to the United States," said White House press secretary Tony Snow in Texas, where U.S. President George W. Bush is taking a 10-day vocation.

    Snow said Bush would address the issue during a visit to Green Bay, Wisconsin later on Thursday. Enditem