Terror Plot Foiled In London

Police in London say they have thwarted a major terrorist plot intended to blow up planes, reportedly over the Atlantic while flying to the U.S. Twenty-one suspects are in custody, after a series of arrests overnight.

U.S. counterterrorism officials say United, American and Continental Airlines were targets of the plot, described by a top British police official as "intended to be mass murder on an unimaginable scale."

CBS News Correspondent Bob Orr says officials will not comment on who, or what group, is behind the plot. One official told CBS News: "We know of no immediate threat to US domestic flights. But, we are taking this very seriously. We view the plot as serious and substantial."

Deputy Commissioner Paul Stephenson says the arrests were in London, its suburbs and in Birmingham, and that searches continue in a number of locations.

Britain's Home Secretary, John Reid, says about a dozen of the the suspects were "very close" to succeeding in the plot, which he describes as "significant" and designed to cause loss of life.

Reid also says the plot was uncovered and foiled by British police who have been conducting an undercover operation for a number of months.

Sky News reports the plot may have involved blowing up 20 planes in mid-air over the Atlantic Ocean.

A British police official, commenting anonymously because of the sensitivity of the case, says the plotters planned for a number of planes to blow up at the same time, while in mid-air on the way to the U.S.

He says the suspects are "homegrown," though it was not immediately clear if all of the people in custody are British citizens. The official says police investigating the foiled attack are working closely with the South Asian community.

Multiple airlines with flights to multiple U.S. airports were at risk, according to a western counterterrorism official. Another official refused to identify the airlines because they were still being notified of the threat but referred to them as the "usual suspects." In the past, U.S. cities with terrorism threats or plots have included Washington, New York, Boston and Los Angeles. Airlines whose planes were hijacked on Sept. 11, 2001, were United Airlines and American Airlines. British Airways has also dealt with numerous threats in recent years.

A U.S. law enforcement official said there have been no arrests in the United States connected to the plot.

A senior U.S. counterterrorism official said authorities believe dozens of people - possibly as many as 50 - were involved in the overseas plot. The plan "had a footprint to al Qaeda back to it," said the official, speaking on condition of anonymity because of the sensitivity of the situation.

The plan involved airline passengers hiding explosives in carryon luggage, the official said. "They were not yet sitting on an airplane," but were very close to traveling, the official said, calling that the plot was "the real deal."

Another Western counterterrorism official, also speaking on condition of anonymity about the highly sensitive investigation, called the investigation "very serious."

"This is the real deal," the official said, adding that the reason "they have taken the action they've done is because you don't know what you don't know."

British Prime Minister Tony Blair's office said in London that the prime minister, vacationing in the Caribbean, briefed President Bush on the situation overnight.

There was no immediate public reaction from the White House. Bush is spending a few days at his ranch near Crawford, Texas.

"The United States and the United Kingdom are fully united and resolute in this effort and in our ongoing efforts to secure our respective homelands," said Chertoff.

U.S. intelligence, particularly the CIA, has been working closely with Britain on the investigation, which has been ongoing for months, the second official said.

That official also says that authorities have not yet arrested or detained all suspects who are believed to be involved in the plot.

As a result of the plot, new security precautions have been put into effect at airports in both England and the United States.

Transport Secretary Douglas Alexander, speaking at a Thursday news conference in London, asked air travelers to show patience and understanding of the new rules, which he says will be in effect "as long as the situation demands."

Heathrow airport, the busiest in Europe, was closed to most European flights Thursday morning. The block on incoming traffic applies to flights of three hours or less, affecting most of the incoming traffic from Europe, according to an airport spokesman.

Air France canceled all morning flights to Heathrow, saying it acted because the airport is "saturated." The French Interior Minister meanwhile cancelled his vacation to return to Paris for an urgent meeting on security, with police and intelligence officials.

Extra security measures in place include a ban on carry-on luggage, including purses too big to fit in a passenger's pocket. Passengers are allowed to take personal items - such as their passport, eyeglasses and cash - so long as they are in see-through plastic bags.

Eyeglass cases are not permitted. There are also rules on medicines: prescription medicines can be taken on board, in an amount necessary for the duration of the flight, unless they are in liquid form, in which case the authenticity of the medicine must be verified.

Contact lenses are allowed, but bottles of contact lens solution – which were eyed years ago as a potential terrorist tool – are not.

Keys are allowed as carry-ons. Electronic key chains are not, and all electric or battery-powered items, including laptops, cellphones, ipods, must be in checked, not carry-on, baggage.

In the U.S., Homeland Security Michael Chertoff says the threat level has been increased to Red – that is, severe - for commercial flights originating in England bound for the U.S., and Orange – that is, high - for all commercial aviation operating in or destined for the U.S.

"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," said Chertoff, in a statement issued just after 3 a.m. "Travelers should also anticipate additional security measures within the airport and at screening checkpoints."

"These measures will continue to assure that our aviation system remains safe and secure," Chertoff added. "Travelers should go about their plans confidently, while maintaining vigilance in their surroundings and exercising patience with screening and security officials."