Iran's Islamic Revolutionary Guard Corps has detained several foreigners, including Britain's second most senior envoy in Tehran, for alleged acts of spying such as taking soil samples in restricted areas, state TV reported on Wednesday.
It did not say when they were detained or whether they were still under arrest. Britain said the reports were "completely false".
"These spies were taking earth samples in Iran's central desert where the Revolutionary Guards' aerospace missile exercises were conducted," state TV said.
Iranian state TV showed what it said was footage of Giles Whitaker and his family in central Iran, where the British diplomat appeared to be taking ground samples.
It reported that it was near an area where a missile test was being conducted by the Guards.
"Whitaker was expelled from the city after apologising," the TV report said.
But a representative of Britain's Foreign Office said: "Reports of the arrest of a British diplomat in Iran are completely false."
Samuel Heath, UK spokesman in the US, tweeted: "He is not even posted in Iran any more."
One of those detained was identified by state TV as the husband of Austria's cultural attache in Iran. Austrian officials were not immediately available to comment.
The TV also showed a picture of a third foreigner, identified as Maciej Walczak, a university professor in Poland, who it said was visiting Iran as a tourist.
The TV report ran footage allegedly showing Mr Walczak and three colleagues collecting earth samples in another area after visiting Iran on a scientific exchange programme.
It said their sample collection also coincided with a missile test, in Iran's southern Kerman province.
The Revolutionary Guards have arrested dozens of dual nationals and foreigners in recent years, mostly on espionage and security-related charges.
Rights groups have accused Iran of trying to win concessions from other countries through arrests on security charges that may have been trumped up.
Tehran denies arresting people for political reasons.