London ? Robbers held up a security van at Heathrow Airport on Monday and escaped with $6.5 million in a variety of currencies that had just arrived from Bahrain, police said.

Police said the driver of the van was attacked by at least two men at the airport’s Terminal 4 at about 6:30 a.m. The robbers forced him to the ground and bound his wrists before transferring the cash into another van.

The money had just arrived on British Airways Flight 124. The theft of the eight red cargo boxes of cash occurred as the 187 passengers left the plane and it was being refueled. Within five minutes, all airport security gates were closed, but the robbers were already gone, police said. Details on who owned the money were not released.

The attack raised questions about the effectiveness of efforts to strengthen security at Heathrow after Sept. 11. It was unclear how the robbers got into an area reserved for airport personnel and how they knew their way around.

The second van was later found abandoned and burned nearby, with no trace of the cash or the suspects. Police said they were seeking two males in connection with the robbery.

The guard suffered shock and wrist injuries.