Continental cancels flight over security fears
British Airways, Air France ground several U.S.-bound planes
Continental Airlines is the third airline this weekend to cancel flights due to security precautions.
British Airways and Air France face renewed terror threats against U.S.-bound flights.
Despite the cancellation of international flights, travelers seem determined not to give in to security fears
(CNN) -- Continental Airlines has canceled Sunday's Flight 17 from Glasgow, Scotland, to Los Angeles, California, because of security concerns, a spokesman for the carrier told CNN on Saturday.
"The flight was canceled because we were unable to obtain the necessary security clearances from the Department of Homeland Security and their international counterparts," David Messing said, reading from a statement released by the airline.
Flight 17 included a stop in Newark, New Jersey.
British Airways and Air France had previously grounded several flights to the United States for security reasons in the wake of possible al Qaeda terror threats involving U.S.-bound aircraft.
British Airways canceled Flight 223 from London's Heathrow Airport to Washington Dulles International Airport on Sunday and Monday, and Flight 207 from London's Heathrow to Florida's Miami International Airport on Sunday.
The return flights from Washington -- Flight 222 -- also will be canceled both days, but the return flights from Miami will continue.
The flights were canceled for security reasons on advice from the British government, an airline spokeswoman said.
Air France canceled two Paris-to-Washington flights for security reasons, the airline said. The flights, both numbered 026, were scheduled to take off Sunday and Monday. The return flights, 027, have been canceled because the aircraft will not be available.
Continental's spokesman didn't elaborate on the cancellation. Messing said 150 passengers were booked on the flight, which would have left Glasgow at 12:15 p.m. and arrived in Los Angeles at 8:35 p.m. (11:35 p.m. ET), after the layover in Newark.
The return flight to Glasgow also will be canceled because there will be no plane available.
A senior U.S. official said the flight was canceled because of information from a credible source, which was corroborated by other intelligence.
The official said someone from the Department of Homeland Security had talked to the airline about security measures. Continental uses air marshals; he would not say whether Continental had planned to have marshals on Flight 17.
The official said the United States does not know how terrorists might attack the planes that have been grounded, but "we know they're targeting these flights."
He also said there is word about another threat that could ground British Airways Flight 223, but no action is planned until there is more information.
"The steps taken today are to preserve our security and to make sure that terrorists don't do harm to the United States or our allies," White House spokesman Trent Duffy said. The United States, Britain and France conferred on the cancellations.
Flight 378 from Paris to Philadelphia International Airport was canceled Saturday for operational, not security, reasons, according to the Air France Web site.
Spokeswomen from British Airways and Air France declined to elaborate on the cancellations.
The moves come as U.S. officials again warn that terrorists might be planning to target international flights to the United States. (Full story)
A senior administration official said Saturday the intelligence that prompted the latest warning gives precise threat information, including airlines, dates and flight numbers.
The intelligence mentioned Air France and British Airways flights to the United States as well as British Airways Flight 223 specifically. That flight was canceled twice in early January based on previous intelligence from an informant and other sources.
Last month, similar threats prompted the cancellation of three Air France flights to Los Angeles, California, on Christmas Eve and Christmas. The return flights were canceled for operational reasons.
At the time, the U.S. national terror threat level was at orange, or high, on the color-coded alert system. The threat level has since been lowered to yellow, or elevated.
British Airways said Flight 207 would have carried 350 passengers and Flight 223 about 170 passengers. Those passengers are being rerouted.
British Airways aircraft sit on the tarmac at Heathrow Airport in London.
Britain's Department for Transport, which advises the airline on security matters, issued a statement on the cancellations:
"Aviation security is being kept under review at all times. In the light of information received, and in discussion with the airline, the decision was made that these flights should be canceled," the agency said.
"Aviation security measures are adjusted from time to time, and occasional cancellations may be necessary. The first priority is always the safety of the traveling public."
A U.S. State Department spokesman told CNN that the United States and Britain "have been working especially closely over the past weeks to identify threats to our citizens, particularly threats to civil aviation, and to develop procedures to counter those threats."
The spokesman said the information relates only to specific flights, not carriers or transatlantic flights in general.
"In some instances, where specific flights may be a higher risk, the carrier or the UK government may choose to cancel those flights. We will in any case work with the UK authorities to assure the continued safety of all carriers on all loops between the US and the UK," the spokesman said.
Also Saturday, a burning smell caused a Virgin Atlantic Airways flight from London to New York to return to Heathrow as a safety precaution more than two hours after it took off, the airline said. (Full story)
The flight was headed to John F. Kennedy International Airport. Passengers were put on later flights.
CNN's Kelli Arena, John King and Jamie McIntyre contributed to this report.