The official said the plotters intended to simultaneously target multiple
planes bound for the United States.
"We think this was an extraordinarily serious plot and we are confident that
we've prevented an attempt to commit mass murder on an unimaginable scale,"
Deputy Police Commissioner Paul Stephenson said.
Prime Minister Tony Blair, vacationing in the Caribbean, briefed President
Bush on the situation overnight, Blair's office said. There was no immediate
public comment from the White House. Bush is spending a few days at his ranch
near Crawford, Texas.
US Homeland Security Secretary Michael Chertoff said the plot had the
hallmarks of an operation planned by al-Qaida, the terrorist group behind the
Sept. 11 attack on the United States.
"It was sophisticated, it had a lot of members and it was international in
scope. It was in some respects suggestive of an al-Qaida plot," Chertoff said,
but he cautioned it was too early in the investigation to reach any conclusions.
It is the first time the red alert level in the Homeland Security warning
system has been invoked, although there have been brief periods in the past when
the orange level was applied. Homeland Security defines the red alert as
designating a "severe risk of terrorist attacks."
"We believe that these arrests (in London) have significantly disrupted the
threat, but we cannot be sure that the threat has been entirely eliminated or
the plot completely thwarted," Chertoff said.
He added, however, there was no indication of current plots within the United
States.
Chertoff said the plotters were in the final stages of planning. "We were
really getting quite close to the execution phase," he said, adding that it was
unclear if the plot was linked to the upcoming fifth anniversary of the Sept. 11
terror attacks.
A senior US counterterrorism official said authorities believe dozens of
people - possibly as many as 50 - were involved in the plot. The
official spoke on condition of anonymity because of the sensitivity of the
situation.
The plan involved airline passengers hiding masked explosives in carry-on
luggage, the official said. "They were not yet sitting on an airplane," but were
very close to traveling, the official said, calling the plot "the real deal."
Passengers in Britain faced delays as tighter security was hastily enforced
at the country's airports and additional measures were put in place for all
flights. Laptop computers, mobile phones, iPods, and remote controls were among
the items banned from being carried on board.
Liquids, such as hair care products, were also barred on flights in both
Britain and the U.S., raising the possibility that authorities were searching
for a liquid explosive.
In the mid-1990s, officials foiled a plan by terrorist mastermind Ramzi
Youssef to blow up 12 Western jetliners simultaneously over the Pacific. The
alleged plot involved improvised bombs using liquid hidden in contact lens
solution containers.
Huge lines formed at ticket counters and behind security barriers at Heathrow
and other airports in Britain.
Ed Lappen, 55, a businessman from Boston, who was traveling with his wife and
daughter to Russia, found himself unable to travel further. "We're safe, we're
OK," he said at Heathrow. "Now my daughter is going to get a shopping trip in
London."
