Washington ? Britain canceled two British Airways flights between London and Washington Thursday amid tightened air security over the holidays that also prompted U.S. officials to forbid a New Year’s Eve flight from Mexico City to Los Angeles and to question passengers for hours who had arrived at Washington-Dulles Airport on a flight from London.

No arrests were made on any of the flights, but the extraordinary New Year’s measures, which included F-16 fighter jet escorts for some foreign carriers flying over U.S. airspace, underscored the concern of U.S. officials that terrorists planned to use international flights to attack American targets.

U.S. aviation and law enforcement officials said Thursday that intelligence has identified a variety of dates, flights and routes that pose an elevated risk. For at least three weeks, officials have been combing through names of passengers ticketed on some flights from Mexico, France and other countries bound for Los Angeles International Airport, Dulles and New York’s John F. Kennedy International Airport, according to one senior aviation official.

Under the high-risk threat alert imposed Dec. 21, Department of Homeland Security and local police also maintained tight security over college football bowl games and New Year’s festivities such as the Tournament of Roses parade. While flight restrictions over Las Vegas and Manhattan were eased Thursday morning, they were still enforced in other places such as Washington.

Overseas flight concerns

U.S. counter-terrorism officials will keep close watch over some flights for the next several weeks, according to a senior aviation official. “They will take appropriate action in the weeks ahead,” the official said. Air security overseas is “not at the level it should be and (U.S.) officials are concerned about it.”

British Airways Thursday canceled Flight 223 from London’s Heathrow Airport to Dulles for unspecified security reasons. The return Flight 222 from Dulles to London also was canceled. Flight 223 on New Year’s Eve was detained at Dulles and its passengers questioned.

Air France Flight 68, a nonstop from Paris to Los Angeles, was canceled last week along with five other Air France departures on the same route after U.S. officials found that some passenger names matched those of suspected terrorists. AeroMexico Flight 490 from Mexico City to Los Angeles was canceled on New Year’s Eve for similar reasons, according to several U.S. officials.

Agustin Gutierrez Canet, spokesman for Mexican President Vicente Fox, said AeroMexico Flight 490 was canceled after the U.S. Department of Homeland Security denied it permission to land in Los Angeles. “They said it was for security reasons but never specifically explained the reasons behind it,” Gutierrez Canet said. He added that U.S. officials directly contacted the airline to request the flight cancellation.

An Aeromexico Airlines plane is seen at a gate at the Mexico City International Airport. An Aeromexico flight from Mexico City to Los Angeles was canceled Wednesday after U.S. authorities said they would refuse to allow it to land, a spokesman for Mexico's president said Thursday.

Gutierrez Canet said 40 passengers booked on the AeroMexico flight flew to Los Angeles later in the day on a flight operated by Mexicana Airlines.

Some Air France and AeroMexico flights have been trailed in U.S. airspace by F-16 fighter jets over the past week to ensure that the planes remain on course, according to U.S. government and aviation officials. Air France, French and Mexican government officials said earlier this week that they have placed air marshals aboard certain U.S.-bound flights.

Passenger detention

FBI and Department of Homeland Security officials said all passengers aboard Wednesday’s British Airways flight were released by early Thursday morning.

“It was an unfortunate occurrence and our apologies are extended to the passengers who were delayed and detained,” said FBI spokeswoman Debbie Weierman. “What was paramount is the safety and security of passengers on the plane.”

Law enforcement officials became concerned about the British Airways flight after it had departed from London. Normally, U.S. officials screen passenger manifests for each incoming international flight before it takes off, but the passenger list for the Dulles flight did not get passed to authorities until after departure, law enforcement sources said Thursday.

Michael Duell of Oakton, Va. gets a hug from his daughters Chrissy, left, and Becky at Dulles airport near Washington. Duell was a passenger Wednesday aboard British Airways Flight 223, which was delayed for several hours as the FBI questioned passengers and searched luggage.

Several names of passengers aboard the flight were identical to those on the FBI’s terrorism database, sources said. Some time after the plane was airborne, U.S. officials notified the pilot that fighter jets would escort it to Dulles and passengers would be questioned and undergo additional security procedures upon arrival, law enforcement and aviation sources said.

There was no specific threat to the British Airways flight, nor did any incident occur on board, the FBI’s Weierman said. “We are running to the ground every specific security issue — anything that would give us any kind of pause,” she said. Screening some passengers upon arrival in the United States is “normal protocol.”

The flight from Heathrow to Dulles on Wednesday was packed with families and children, passengers said. The plane circled the airport for about 15 minutes because the pilot told passengers it did not have clearance to land.

After landing, the plane parked in a secure area and passengers sat for about an hour and a half with no idea of what was happening.

“This was a case of detention without due process,” said David Litwack, 59, of Fairfax, Va., an information technology consultant. “If I am suspect of something, I expect to have allegations read to me. None of that was done. (It was) purely whimsical, as far as we could tell.”