"On the advice of the police and security services, the Treasury has instructed the Bank of England to issue notices to effect a freeze of the assets of a number of individuals arrested in yesterday's operations," a Treasury statement said.
Most of those named in the list are London residents, and many have Muslim names.
Also Friday, intelligence agents arrested at least five people, including two British nationals of Pakistani origin, accused of having provided information for the plot, according to a senior government official.
The arrests were made in the eastern city of Lahore and in Karachi, Pakistan's main port on the Arabian Sea, the official said on condition of anonymity because he did not have authority to speak formally on the issue.
Two were Britons arrested a week ago, he said. The five Pakistanis were arrested on suspicion that they served as local "facilitators" for the two Britons, the official said. It wasn't clear when they'd been detained.
British Home Secretary John Reid says the threat level in Britain remains at the highest level, and officials are grateful for cooperation from Pakistan.
Late Thursday, a federal law enforcement official in Washington said at least one martyrdom tape - typically, a video starring a suicide attacker and lionizing the individual shortly before a planned attack - was found during ongoing raids across England on Thursday. Such a tape, as well as the scheme to strike a range of targets at roughly the same time, is an earmark of al Qaeda and several other militant Islamic groups.
The terrorist attack foiled by British authorities on Thursday was aimed at blowing up as many as 10 airplanes on trans-Atlantic flights, and plotters hoped to stage a dry run within two days, according to U.S. intelligence officials.
The actual attack would have followed within days.
One official said the suicide attackers planned to use a peroxide-based solution that could ignite when sparked by a camera flash or another electronic device.
The test run was designed to see whether the plotters would be able to smuggle the needed materials aboard the planes, these officials said. They spoke only on condition of anonymity because of the sensitivity of the subject matter.
British authorities said the attack would have used explosives smuggled in hand luggage. Police described the plot as "mass murder on an unimaginable scale."
Britain said 21 people were arrested overnight, including the alleged "main players" in the plot. The scheme involved 10 flights, one U.S. counter-terrorism official said.
At least 24 people are now in custody — most of them British-born and of Pakistani descent. The youngest suspect is just 17. The police are searching for at least five more suspects, reports CBS News correspondent Sheila MacVicar from London.
CBS News confirmed that one of the arrested men was a Heathrow Airport worker taken from his home by police in his airport uniform. Also, four arrests were made in Pakistan in recent days, two of them "very important," according to officials.
"This country is safer than it was prior to 9/11. We've taken a lot of measures to protect the American people, but obviously we're not completely safe," President Bush said Thursday from an airport tarmac in Green Bay, Wis. "It is a mistake to believe there is no threat to the United States of America."
The president also laid the blame for the foiled attack squarely on al Qaeda-type terrorism.
"This nation is at war with Islamic fascists who will use any means to destroy those of us who love freedom, to hurt our nation," Mr. Bush said.
Pakistan intelligence helped British security agencies crack the terrorist plot, a government and an intelligence official said Thursday. The intelligence official said an Islamic militant arrested near the Afghan-Pakistan border several weeks ago provided a lead that played a role in "unearthing the plot," that helped authorities arrest suspects in Britain.
French Interior Minister Nicolas Sarkozy said in Paris that the plotters "appear to be of Pakistani origin."
The U.S. issued its highest terrorism alert ever, red, for commercial flights from Britain to the United States and raised the threat level for all domestic and international flights. All other flights, including all domestic flights in the United States, were put under an orange alert, one step below the highest level.
"No liquids or gels of any kind will be permitted in carry-on baggage. Such items must be in checked baggage. This includes all beverages, shampoo, sun tan lotion, creams, toothpaste, hair gel and other items of similar consistency," a Homeland Security statement.
Homeland Security Secretary Michael Chertoff said the terrorists planned to use liquid explosives disguised as beverages and other common products and. They planned to combine the products once the planes were aloft to create and detonate explosive devices. Sources tell CBS News correspondent Jim Stewart that these chemical bombs would have been set with timers to go off simultaneously.
"This is not a case of wannabes fantasizing about an attack. We believe it was the real deal. To target multiple airlines with such a plan requires a sophistication that strongly points to al Qaeda," a senior U.S. official told Stewart.
The investigative file put together by Scotland Yard shows the case began three months ago when two British citizens of Pakistani descent traveled to Pakistan and met with Islamic extremists. Following the men led agents to their associates back in the London area (approximately 20 to 30 young men described as "disaffected" British nationals mostly of Pakistani descent). A British undercover agent apparently infiltrated the group, Stewart reports.
Then, two weeks ago it became apparent the group was targeting aircraft and the investigation took on new urgency. When investigators became convinced the men had picked their flights and bought battery-powered charging devices to set off their bombs, they moved in, reports Stewart.
White House spokesman Tony Snow said, "There were some signs. They thought it was time to move," he said of British authorities.
Chertoff said the plot is "suggestive of an al Qaeda plot," and that the plotters were in the final stages to execute all elements of this plan. He added that there was no indication of plotting in the United States and that it was unclear whether the alleged plot was linked to the upcoming fifth anniversary of the Sept. 11 attacks.
London Deputy Commissioner Paul Stephenson says the arrests were made in London, its suburbs and in Birmingham, and that searches continue in a number of locations. "We are confident that we've prevented an attempt to commit mass murder on an unimaginable scale," Stephenson said.
Britain's home secretary, John Reid, said about a dozen of the suspects were "very close" to succeeding in the plot, which he describes as "significant" and designed to cause loss of life. The threat level in England has, for the first time ever, been raised to critical. That means the threat of an attack is imminent, MacVicar reports.
Peter Clarke, head of the Metropolitan Police anti-terrorist branch, said surveillance had been carried out for months before police arrested the 21 people overnight. Sources tell Stewart that several of the 21 suspects picked up may not have been actual bombers, but people with material knowledge of the plot.
"We have been looking at meetings, movements, travel, spending and the aspirations of a large group of people," Clarke said. "All the arrests were made on suspicion of the commission, preparation or instigation of acts of terrorism."
British Airways canceled all flights between Heathrow Airport and points in Britain, Europe and Libya for all of Thursday. Extra security measures in place at airports leaving Britain include a ban on carry-on luggage, including purses too big to fit in a passenger's pocket. Passengers are only allowed to take personal items — such as passport, eyeglasses and cash — if they are in see-through plastic bags.
A British police official 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.
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.
"We cannot assume that this threat has been completely thwarted," Chertoff said. "There's sufficient uncertainty as to whether the British have scooped up everybody."
As a result of the plot, new security precautions have been put into effect at airports in both England and the United States. Guards armed with rifles stood watch in several airports, and the governors of California, New York and Massachusetts said they were sending National Guard troops to bolster security.
Airlines in South Korea, Singapore, Japan and Australia imposed new restrictions on carry-on and other luggage for jets in accordance with requests from American and British authorities.