British police said Thursday a terror plot against U.S. airlines uncovered in London was "an attempt to commit mass murder on an unimaginable scale."
Paul Stephenson, deputy commissioner of London's Metropolitan Police, said at a news conference that terrorists had planned to cause "untold death and destruction" by blowing up several aircraft mid-flight between the U.K. and the United States.
He added, "We believe that the terrorists' aim was to smuggle explosives on to planes in hand luggage and to detonate them in flight." He said 21 people had been arrested overnight.
British Prime Minister Tony Blair is reportedly in discussions with President Bush about the situation.
"The alleged plot has global implications," said Peter Clarke, head of the British police's anti-terrorism branch. "The people arrested remain in custody in London. Searches are underway of business and other premises in London and elsewhere."
A U.S. administration official said airlines targeted include Continental, United and American, CNN reports. Officials speaking to NBC News said that New York City appeared to be the main target of the intended attacks.
Since the news broke, a ripple effect has taken place at the world's airports. Massive flight delays are already in effect in Europe, with major disruptions expected on American travel routes. Passengers set to fly out of New York City's John F. Kennedy Airport have been advised to arrive for flight check-in at least three hours before departure.
"We believe that these arrests have significantly disrupted the threat, but we cannot be sure that the threat has been entirely eliminated or the plot completely thwarted," Homeland Security Secretary Michael Chertoff said in a statement, the Associated Press reports.
Chertoff said that the threat level for international flights between Britain and the U.S. has been raised to the highest "severe or red" level, and "to defend further against any remaining threat from this plot, we will also raise the threat level to high, or orange, for all commercial aviation operating in or destined for the United States."
Chertoff added that "currently, there is no indication ... of plotting within the United States," but that beefed-up security at U.S. airport checkpoints would take effect Thursday at 4 a.m. local time across the country and will remain in place as warranted.
At an 8 a.m. news conference Thursday, Chertoff called the terror plot "well planned, well advanced, and involving a significant amount of operatives disguised as passengers." He also said that officials are waiting until all the facts are in before labeling the plan the work of al Qaeda.
Chertoff said airports will enforce a temporary ban of all liquids in aircraft cabins, with exception of baby formulas and medicines, which must be presented at security checkpoints for inspection. He also advised travelers to pack as little carry-on baggage as possible and to call airlines for suggested arrival times.
Chertoff added that updates on the situation are expected over the next several days.
At London's Heathrow Airport, all European inbound flights have been canceled, and outgoing passengers are prohibited from bringing any hand luggage aboard, including cellphones, iPods and handbags, airport authorities said.
All liquids are banned on board except for essential medicines. Milk for babies will be allowed on board but must be tasted by the accompanying passenger, the British Airports Authority said in a statement.
JFK Airport is following suit, with beverages, liquids and hair gels among the banned substances.
Paul Stephenson, deputy commissioner of London's Metropolitan Police, said at a news conference that terrorists had planned to cause "untold death and destruction" by blowing up several aircraft mid-flight between the U.K. and the United States.
He added, "We believe that the terrorists' aim was to smuggle explosives on to planes in hand luggage and to detonate them in flight." He said 21 people had been arrested overnight.
British Prime Minister Tony Blair is reportedly in discussions with President Bush about the situation.
"The alleged plot has global implications," said Peter Clarke, head of the British police's anti-terrorism branch. "The people arrested remain in custody in London. Searches are underway of business and other premises in London and elsewhere."
A U.S. administration official said airlines targeted include Continental, United and American, CNN reports. Officials speaking to NBC News said that New York City appeared to be the main target of the intended attacks.
Since the news broke, a ripple effect has taken place at the world's airports. Massive flight delays are already in effect in Europe, with major disruptions expected on American travel routes. Passengers set to fly out of New York City's John F. Kennedy Airport have been advised to arrive for flight check-in at least three hours before departure.
"We believe that these arrests have significantly disrupted the threat, but we cannot be sure that the threat has been entirely eliminated or the plot completely thwarted," Homeland Security Secretary Michael Chertoff said in a statement, the Associated Press reports.
Chertoff said that the threat level for international flights between Britain and the U.S. has been raised to the highest "severe or red" level, and "to defend further against any remaining threat from this plot, we will also raise the threat level to high, or orange, for all commercial aviation operating in or destined for the United States."
Chertoff added that "currently, there is no indication ... of plotting within the United States," but that beefed-up security at U.S. airport checkpoints would take effect Thursday at 4 a.m. local time across the country and will remain in place as warranted.
At an 8 a.m. news conference Thursday, Chertoff called the terror plot "well planned, well advanced, and involving a significant amount of operatives disguised as passengers." He also said that officials are waiting until all the facts are in before labeling the plan the work of al Qaeda.
Chertoff said airports will enforce a temporary ban of all liquids in aircraft cabins, with exception of baby formulas and medicines, which must be presented at security checkpoints for inspection. He also advised travelers to pack as little carry-on baggage as possible and to call airlines for suggested arrival times.
Chertoff added that updates on the situation are expected over the next several days.
At London's Heathrow Airport, all European inbound flights have been canceled, and outgoing passengers are prohibited from bringing any hand luggage aboard, including cellphones, iPods and handbags, airport authorities said.
All liquids are banned on board except for essential medicines. Milk for babies will be allowed on board but must be tasted by the accompanying passenger, the British Airports Authority said in a statement.
JFK Airport is following suit, with beverages, liquids and hair gels among the banned substances.
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