LONDON — British officials identified 19 of the suspects accused of planning to blow up U.S.-bound aircraft in the biggest terrorist plot to be uncovered since 9/11. Travelers saw shorter lines at airports as flight schedules slowly returned to normal today.

Five Pakistanis have been arrested in Pakistan as suspected "facilitators" of the plot, a government official said, in addition to two Britons arrested there about a week ago.

The Bank of England said it had frozen the accounts of 19 people arrested Thursday. The men, ranging in age from 17 to 35, had names of Muslim origin, many of which are common in Pakistan.

British police have arrested 24 people suspected of involvement in the plot. Investigators, describing a plan on the scale of the Sept. 11 attacks, said the attackers planned to use common electronic devices to detonate liquid explosives to bring down as many as 10 planes.

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 told The Associated Press. The officials spoke on condition of anonymity because Britain asked that no information be released.

A federal law enforcement official in Washington said that at least one martyrdom tape was found during 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 a hallmark of al-Qaida.

British Home Secretary John Reid said Britain was grateful for Pakistan's cooperation and that officials believed the main suspects were in custody. However, the threat level in the U.K. remained at "critical," the highest level.

Agents in Pakistan arrested at least seven people, including two British nationals of Pakistani origin who provided information on the terror plot, a senior government official said today. The arrests were made in the eastern city of Lahore and in Karachi, the official said on condition of anonymity because he did not have the authority to speak formally on the issue.

Two were Britons arrested about 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.

The Guardian newspaper, citing unidentified British government sources, said that after the arrests a message was sent to Britain telling the plotters: "Do your attacks now." That message was intercepted and decoded earlier this week, The Guardian said.

A U.S. congressman briefed by intelligence officials, who did not want to be identified because of the sensitivity of the investigation, said U.S. intelligence had intercepted terrorist chatter.

Many of the 24 suspects arrested in Britain were said to be British Muslims, and neighbors said at least two of those arrested were converts to Islam. One of the suspects was reported to work at Heathrow Airport.

Airline passengers faced a second day of disruptions and disappointment as airports struggled to restore flight schedules.

"It is going to be another difficult day today, both for airports and for passengers, but there is cause for optimism that we will get more flights off today," said Stephen Nelson, chief executive of British Airports Authority, which runs Britain's major airports.

At Heathrow, Europe's busiest airport, around 70 percent of flights were running, and most inbound flights arrived on time, though flights from the United States — which increased security measures in the wake of the threat — were heavily delayed.

New security measures banning liquids and gels on flights remained in place.

"I quite understand all the checks. I know why they have got to do it," said Elaine Loman, who was hoping to catch a flight from Heathrow to Barcelona, Spain.

The threat of liquid explosives led to a ban on carrying nearly any kind of fluid aboard an aircraft. Mothers tasted baby bottles in front of airport security guards to prove it contained milk or formula — not a component of an explosive.

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.

Targeted were United, American and Continental flights from Britain to major U.S. destinations, which counterterrorism officials said probably included New York, Los Angeles and Washington. Los Angeles Mayor Antonio Villaraigosa said the individuals plotted to detonate liquid explosive devices on as many as 10 aircraft.