The flight cancellations added to Christmas holiday tensions that have been high since President Bush raised the national terror alert level to orange, the second highest level, on Sunday. US security officials have been closely monitoring activity at airports, train stations and public buildings. Police randomly stopped cars near the US Capitol on Wednesday.

The Air France flights, scheduled for Wednesday and Thursday, were canceled after US officials passed on information they deemed credible about security threats from passengers flying from Paris to Los Angeles, US and European officials said Wednesday.

Three of the canceled flights were headed to Los Angeles and three more were returning to Paris.

A spokesman for French Prime Minister Jean-Pierre Raffarin said the decision to cancel the flights came early Wednesday after American authorities notified France that "two or three" suspicious people, possibly Tunisian nationals, were planning to board the flights.

The French Interior ministry said the United States handed French authorities the names of suspicious people who may have intended to board the flights but no people by those names went through airport security checks, and no arrests were made. French television station LCI reported that US authorities believed members of al-Qaeda may have been planning to board the planes.

It was unclear who ordered the cancellations. The Interior Ministry said the flights were canceled at the request of the US Embassy in Paris. A spokesman for Raffarin said the United States had threatened to refuse the planes permission to land if they took off. But US officials refused to confirm that they had requested the cancellations.

However, French justice and law enforcement officials said yesterday they found little evidence that terrorists were planning to use US-bound aircraft to launch attacks against American targets.

No arrests were made, and French authorities released seven men -- one French, one American and several Algerians -- after briefly questioning them late Wednesday, said an Interior Ministry spokesman. He said the investigation was all but on hold.