Pentagon spokesman John Kirby told NBC News there was "no reason to doubt the authenticity" of the clip purporting to show US soldier Sergeant Bowe Bergdahl, who has spent five years in Taliban captivity, being handed back into US custody.
He said: "US officials are currently reviewing the video, but our focus right now is in getting Bergdahl the care he needs."
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In her message Theresa May praised the "inspirational bravery" and "unbreakable spirit" of Mancunians in the wake of the blast.
ITV News has obtained exclusive footage of the moment armed police raided a house believed to be linked to the Manchester suicide bomber.
The Manchester Evening News set up a JustGiving page asking people to support the families of those affected by the suicide bombing.