Iran's president Mahmoud Ahmadinejad claims he has been blocked by the UK authorities from attending the Olympic Games in London.
Mr Ahmadinejad told Iran's official news agency IRNA that he would like to be "beside Iranian athletes" at the Games, but that Britain has "a problem" with him being there.
The Foreign Office today refused to confirm or deny his claim, saying only: "We don't comment on individual cases."
The row comes ahead of talks in Baghdad next week over Iran's controversial nuclear programme, which Britain and other international powers suspect is intended to produce an atomic weapon. Tehran denies the charge, insisting it wants only to develop a civilian nuclear power capability.
The E3+3 nations - Britain, France, Germany, the US, Russia and China - will meet with negotiators from Iran in the Iraqi capital for a day of talks on May 23.
The meeting follows on from talks in Istanbul last month at which the E3+3 team detected signs of willingness on the Iranian side to engage constructively after a long stalemate.
Britain believes that the EU embargo on Iranian oil, agreed in January and due to come into effect in July, is having a significant effect in concentrating minds in Tehran.
Negotiators are expected to set out details in Baghdad of what Iran must do in order to ratchet down pressure and benefit from the co-operation of the international community on its civilian nuclear energy aspirations.
It is thought unlikely that the withdrawal of the oil embargo will be on the table unless there are signs of dramatic concessions from Tehran.
Britain cut diplomatic ties with Iran last year after militant students stormed its embassy in Tehran.