British Airways said tonight it had cancelled a London-Riyadh flight scheduled to leave tomorrow, for security reasons.

The airline said in a statement that following the cancellation of last Wednesday's flight from Heathrow to Riyadh in Saudi Arabia, it had cancelled tomorrow's flight to Riyadh.

BA said a British government team, led by the Department of Transport, was working closely with the Saudi authorities.

Flight BA 263 had been due to leave at 1.35pm; the return flight on Sunday, BA 262, will also be cancelled.

BA earlier cancelled today's afternoon flight from London to Washington for a second consecutive day after receiving what has been described as 'security advice' from the British government.

The announcement for flight BA 223 was made as passengers for the flight were checking in at Heathrow Airport.

The plane had been due to leave at 3.05pm, but BA announced it had been cancelled at 1.15pm - less than two hours before take off.

Yesterday's flight BA223 was also cancelled several hours before it was scheduled to depart after BA received security advice from the Government.

On New Year's Eve, the same flight had been kept on the runway for three hours after landing at Washington Dulles International Airport to allow security officials to board the plane and question passengers.

The Boeing 747 was escorted into Dulles by two F-16 fighter jets.

An Aeromexico flight from Mexico City to Los Angeles was also cancelled after US authorities refused to allow it to land.

Flight 490 was cancelled after Homeland Security officials said they were concerned it might be a safety risk, according to a spokesman for Mexico's President Vicente Fox.