London Mayor Boris Johnson said that Russian President Vladimir Putin should "strip to the waist" and take part in the Olympic judo event.
Mr Putin, who holds a black belt in the martial art, will visit Downing Street before heading to the Olympic Park.
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It will be a cloudy and at times damp morning across much of the UK, apart from the far west where it will be dry and bright.
Barack Obama has returned to the political spotlight, campaigning for Democratic candidates ahead of upcoming elections.
The prime minister said there was a "clear and urgent imperative" to give new impetus to stalled negotiations.