Flights BA 223 from London Heathrow to Washington on Sunday and Monday and flight BA 207 to Miami on Sunday were grounded on government advice.

Air France later said it was cancelling two Paris to Washington flights.

The move comes after US officials said fresh intelligence showed BA and Air France flights could be hijacked by al-Qaeda and crashed into US targets.

A BA spokeswoman said safety was the airline's top priority.

"The safety and security of our operations is our absolute priority and will not be compromised," she said.

Chris Yates, aviation and security editor for Jane's Transport, told the BBC the reason for the cancellations could be a result of people returning from the Hajj pilgrimage in Saudi Arabia.

He said: "Many Muslims will be travelling throughout aviation systems over the next few days, and some names may match or be similar those held on security records in the US."

Asked why passengers could not simply arrive early at airports to allow time to be cleared by security instead of having their flights cancelled, he said such a move "would create congestion in many airports all around the world".

Air France flights AF026 were cancelled Sunday and Monday "for reasons of security," spokeswoman Veronique Brachet said.

BA's Flight 223 had been the subject of concern early in January, when it was cancelled twice because of security fears and then delayed for hours several more times.

US officials said on Friday new intelligence indicated BA Flight 223 and Air France flights from Paris to an unspecified US city could be terrorist targets.