Iranian media reports that the Revolutionary Guards had arrested several foreign diplomats for espionage sowed confusion Thursday, after two of the countries concerned denied that their nationals had been detained.

While Poland on Thursday confirmed a scientist was in Iranian custody, Austria strongly rejected reports that any of its diplomats had been held, mirroring an announcement by Britain late Wednesday.

The developments coincide with heightening tensions between Tehran and world powers over stalled attempts to revive a 2015 nuclear deal and a recent uptick in confirmed detentions of Western nationals in Iran.

On Wednesday, Iran's Fars news agency and state television had reported that the Revolutionary Guards arrested -- on an unspecified date -- several foreign diplomats.

"The Revolutionary Guards' intelligence service identified and arrested diplomats from foreign embassies who were spying in Iran," Fars said, adding that a British diplomat named by state television as deputy head of mission Giles Whitaker was subsequently expelled.

London swiftly denied its deputy ambassador had been arrested, and on Thursday, Britain's ambassador to Iran said the envoy had left the country last year.

"These reports that our Deputy Ambassador is currently detained are very interesting... He actually left Iran last December, at the end of his posting," British ambassador Simon Shercliff wrote on Twitter.

Map of Iran showing main nuclear facilities
Map of Iran showing main nuclear facilities AFP / Simon MALFATTO

Iranian state television accused him of "carrying out intelligence operations" in military areas.

A state TV journalist said the diplomat "was among those who went to the Shahdad desert with his family as tourists", referring to an area in Kerman province.

The Shahdad desert, a rocky and mountainous district with ancient ruins some 810 kilometres (500 miles) southeast of Tehran, is a popular place for foreigners to visit.

While Fars said the Briton was expelled from Iran, state television said he was only expelled from "the area" the diplomats were arrested in.

Before Shercliff's comment, Britain's foreign ministry had already categorically denied its deputy ambassador had been detained, calling the reports "completely false".

In this file photo taken on August 21, 2019 a cloud-based console is displayed at the Microsoft Xbox stand during the Video games trade fair Gamescom in Cologne, western Germany
In this file photo taken on August 21, 2019 a cloud-based console is displayed at the Microsoft Xbox stand during the Video games trade fair Gamescom in Cologne, western Germany AFP / Ina FASSBENDER

Vienna also denied reports in Iranian media claiming that Ronald Geschirr, who it called "the spouse of the Austrian embassy's cultural adviser", was among those arrested.

"Regarding the media reports: All employees and their relatives in Tehran are doing well, nobody was arrested," an Austrian foreign ministry spokeswoman told AFP.

But Poland's foreign ministry spokesman Lukasz Jasina confirmed Thursday that "a Polish citizen was deprived of liberty in Iran in September 2021", identifying the detainee only as a "recognised scientist", without naming him.

"Consular and diplomatic actions are being taken to allow our citizen to return to Poland as soon as possible", Jasina added, noting Warsaw was in contact "with allied countries", without providing details, but asking that the family's privacy be respected.

Iran's state television showed images of a man it identified as "Maciej Walczak, head of the microbiology department" at the Nicolaus Copernicus University in Torun in Poland.

"This university is linked to the Zionist regime," it said, referring to arch-enemy Israel, which is staunchly opposed to the 2015 nuclear agreement between Iran and world powers, perceiving it as a threat to its security.

Walczak "entered Iran with three other people in the context of scientific exchanges but he went to the desert region of Shahdad as a tourist while missile tests were being carried out", state television said. It said he took rock and soil samples.

But Marcin Czyzniewski, a spokesman for the university where Walczak is reported to be an expert in environmental microbiology, said it was "an old story".

"Iran cites the names of three people, two of whom have returned to Torun for months," Czyzniewski said.

Tensions between Iran and Western powers have lately increased as talks in Vienna to revive the 2015 nuclear deal have been stalled since March.

The US walked out of the deal in 2018 under then president Donald Trump, who proceeded to reimpose biting sanctions on Tehran, prompting the latter to step away from many of the nuclear commitments it made under the accord.

Qatar last week hosted indirect talks in Doha in a bid to get the Vienna process back on track, but those discussions broke up after two days without any breakthrough.

Over a dozen Western nationals are held in Iran, including a French couple detained in May, in what activists argue is a policy of hostage-taking aimed at extracting concessions from the West.