Air France has resumed flights between Paris and Los Angeles, after a terror scare that grounded six planes on Wednesday and Thursday.
US officials were concerned by names on passenger lists
An Air France jet left Paris's Charles de Gaulle airport for Los Angeles on Friday, after a three-hour delay due to extra security checks.
The flights were suspended amid fears of al-Qaeda attacks over Christmas.
But the French authorities said they had no evidence of plans to use aircraft to attack US targets.
Hundreds of passengers were left stranded in Paris and Los Angeles for two days.
The cancellations were announced on Wednesday, after the US Department of Homeland Security spoke of a "credible threat" from al-Qaeda operatives due to board a flight from Paris to Los Angeles.
On Thursday French intelligence questioned several people booked on the suspended flights, but said they had found no links to militants.
However on Friday US officials said militants might still be plotting a repeat of the 11 September 2001 attacks on the United States.
The US Government has raised the national threat level from Elevated to High Risk of terrorist attack over the holiday period.
French police checked Paris airports
US Homeland Security officials are reported to be angry that the French Government cancelled the flights publicly.
An unnamed official told the Associated Press news agency that security forces had been "hoping that we would be able to lure some of these people in".
Terrorism expert Walter Purdy, of the Terrorism Research Center in the US, told BBC News the intelligence could have been better used to arrest the suspects at the airport.
US investigators still want to speak to a small number of people in Paris who failed to turn up for boarding the cancelled flights, according to an unnamed US official quoted by AP.