By LARA JAKES JORDAN
The U.S. government raised its threat warning to the highest level for commercial flights from Britain to the United States early Thursday in response to a terror plot uncovered in London. Multiple flights to multiple American cities were put on alert, a western counterrorism official said.
In addition to the highest alert for flights from Britain, the alert for all flights coming or going from the United States was also raised slightly. The government said it was banning beverages, hair gels and lotions from flights, explaining only that liquids emerged as a risk from the investigation in Britain.
"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," said Homeland Security Secretary Michael Chertoff in announcing that the threat level for flights from Britain to the United States has been raised to the highest "severe or red" level.
"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 said.
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."
A statement issued by Chertoff said "currently, there is no indication … of plotting within the United States."
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 and as many as 50 were involved or connected to the overseas plot that was unraveled Wednesday evening. The plan "had a footprint to al-Qaida back to it," said the official, speaking on condition of anonymity because of the sensitivity of the situation.
It was not believed to be connected to the Egyptian students who disappeared in the United States more than a week ago before reaching a college they were supposed to attend in Montana. Three of the 11 have since been found and the FBI has said neither they nor the still-missing eight are believed to be a threat.
The plan involved airline passengers hiding masked 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 the plot "the real deal."
Another Western counterterrorism official, also speaking on condition of anonymity about the highly sensitive investigation, called the investigation "very serious."
U.S. intelligence has been working closely with the British on the investigation, which has been ongoing for months, the second official said.
Authorities have not yet arrested or detained all suspects who are believed to be involved in the plot, the official said, prompting Chertoff’s alarm.
"Consistent with these higher threat levels, the Transportation Security Administration is coordinating with federal partners, airport authorities and commercial airlines on expanding the intensity of existing security requirements," Chertoff said.
"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."
He said the changes take effect at 4 a.m. local time across the United States and will be undated as warranted.
Chertoff said travelers in the United States "should also anticipate additional security measures within the airport and at screening checkpoints."
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.
"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."
Prime Minister Tony Blair’s office said in London that the prime minister, vacationing in the Caribbean, had 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 Homeland Security Department devised the alert system after the Sept. 11 attacks. The last time the U.S.government raised the terrorist risk here to orange, or high, was in July 2005 after the subway bombings in London. It was lowered to yellow a month later, the elevated risk status that has been the norm since the system was created.
U.S. authorities, including the Transportation Security Administration, planned a news briefing early Thursday.
In London, Britain’s Home Secretary John Reid said the alleged plot was "significant" and that terrorists aimed to "bring down a number of aircraft through mid-flight explosions, causing a considerable loss of life."
Police arrested a number of people overnight in London after a major covert counterterrorism operation that had lasted several months, but did not immediately say how many. Heathrow airport in London was closed for most European flights.
The national threat level in Britain was raised to critical _ a warning level that indicates the likelihood of an imminent terrorist attack. The threat rating was posted on the Web site of Britain’s MI5 _ the British domestic spy agency.
Associated Press writers Katherine Shrader and Mark Sherman contributed to this report.