US security agents are to be based at Heathrow and some other UK airports for the duration of the Olympic Games, according to Sky sources.
The Department for Transport has reached an agreement with the US Transportation Security Administration for specialist agents to be based at several UK airports.
They will arrive one week before the Olympics, and leave around a week after the end of the Paralympics.
Sky's Home Affairs correspondent Mark White said: "This is an added security layer that has been done to help boost and aid the American airlines in particular that fly in and out of the likes of Heathrow and other airports.
"Nonetheless it is a very unusual occurrence and is significant."
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