Authorities arrested 24 people in connection with the plot, with more arrests expected.
LONDON -- Chilling accounts leaked by investigators Thursday described a plan on the scale of 9-11 that would use common electronic devices to detonate liquid explosives concealed in sports drink bottles to bring down as many as 10 planes in a nearly simultaneous strike.
British police said they thwarted a terrorist plot, possibly just days away, to blow up U.S.-bound jetliners over the Atlantic and kill thousands.
The bombs were to be assembled on the aircraft apparently with peroxide-based solution and everyday carry-on items such as a disposable camera or a music player, two American law enforcement officials said. The officials spoke on condition of anonymity because Britain asked that no information be released.
British authorities arrested 24 people based partly on intelligence from Pakistan, where authorities detained up to three others several days earlier. More arrests were expected, the official said. The suspects were believed to be mainly British Muslims, at least some of Pakistani ancestry.
A senior U.S. counterterrorism official said the suspects, whose ages ranged from 17 to the mid-30s, were looking to sneak at least some chemicals on the planes in sports drink bottles. Teams of at least two or three men were assigned to each flight, the schedules for which they had researched on the Internet, the official said.
Two other U.S. officials said British, American and Pakistani investigators were trying to trace the steps of the suspects in Pakistan.
Experts said the nature of the plot could herald a new age of terrorism where attackers have access to explosives that are easy to carry and conceal. Emergency security measures quickly implemented on Thursday provided a stark vision of the possible future of air travel.
Mothers tasted baby food in front of airport security guards to prove it contained no liquid explosives. Liquids and gels were banned from flights.
The raids in Britain on Thursday followed a monthslong investigation, but U.S. intelligence officials said authorities moved quickly after learning the plotters hoped to stage a practice run within two days, with the actual attack expected just days after that.
The test run was designed to see whether the plotters would be able to smuggle the needed materials aboard the planes, the officials said, speaking on condition of anonymity.
The plane bombings could have come just ahead of the fifth anniversary of the Sept. 11 attacks carried out by al-Qaida. The terror group's leader Osama bin Laden and his No. 2, Ayman al-Zawahri, are believed hiding along the Pakistan-Afghanistan border and have repeatedly issued tapes threatening new attacks.
"In terms of scale, it was probably designed to be ... a new Sept. 11," said Jean-Charles Brisard, a French private investigator who works with lawyers of many Sept. 11 victims. "It involved the same tools, the same transportation tools and devices."
The close call also shifted attention once more to Britain's Islamic community just over a year after the London transit attacks. Three Britons of Pakistani descent and a Jamaican convert to Islam carried out those deadly bombings with a peroxide-based explosive that trained operatives can make using ordinary ingredients such as hair bleach.
In Pakistan, an intelligence official said the arrest of an Islamic militant near that border several weeks ago played a role in "unearthing the plot." The official, who spoke on condition of anonymity, said some suspects arrested in Britain were linked to al-Qaida. However, authorities stopped short of accusing al-Qaida directly for the plot.
A senior Pakistani government official, also speaking on condition of anonymity because he was not authorized to comment on the matter, said "two or three local people" suspected in the plot were arrested a few days ago in the Pakistani cities of Lahore and Karachi.
French Interior Minister Nicholas Sarkozy said the group "appears to be of Pakistani origin," but did not give a precise source for the information. Britain's Home Office refused comment.
A British police official, speaking on condition of anonymity because of the sensitivity of the investigation, said the suspects were "homegrown," though it was not immediately clear if all were British citizens. He said authorities were working with Britain's large South Asian community.
Tariq Azim Khan, the Pakistani minister of state for information, said "these people were born and brought up in the United Kingdom. Some of them may have parents who were immigrants from Pakistan."
Raids were carried out at homes in London, the nearby town of High Wycombe and in Birmingham, in central England. Searches continued throughout the day, and police cordoned off streets in several locations. Police also combed a wooded area in High Wycombe.
Hamza Ghafoor, 20, who lives across the street from one of the homes raided in Walthamstow, northeast of London, said police circled the block in vans Wednesday and that they generally swoop into the neighborhood to question "anyone with a beard."
"Ibrahim didn't do nothing wrong," Ghafoor said, referring to a suspect. "He played football. He goes to the mosque. He's a nice guy."
The British government raised its threat assessment to its highest level -- critical -- which warns that a terrorist attack could be imminent. The U.S. government, following suit, raised its threat assessment to red alert, also its highest level, for commercial flights from Britain to the United States.
Associated Press Writers Pat Milton and Tom Hays in New York, Lara Jakes Jordan in Washington and Jay Lindsay in Boston contributed to this report.