Details of suspects revealed on 'day after'

The Guardian newspaper, citing unidentified British government sources, said after the first two arrests were made in Pakistan, 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.

Authorities pressed ahead Friday with efforts to smash the purported terror ring. Two U.S. officials said British, U.S. and Pakistani investigators were trying to trace the steps of the suspects in Pakistan and determine whether some of them attended terrorist training camps there.

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, although flights from the United States — which increased security measures in the wake of the threat — were heavily delayed.

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.

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.

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."