During his meeting with Labour leader Ed Miliband in Westminster, Mitt Romney was asked about Olympic security issues and the error over the North Korean team flag.
Mr Romney told ITV News' Lucy Manning that "It is impossible for absolutely no mistakes to occur...As soon as the Games begin, we all forget the organisers and focus on the athletes."
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The town was where the US military and Kurdish fighters first united to defeat the Islamic State group four years ago.
MPs are expected to debate the deal on Saturday.
The duchess is expected to speak at the event, which will involve games, music and traditional Pakistani cakes.