Iran has started prosecuting a French man arrested last year on espionage charges, lawyer Saeid Dehghan wrote on Twitter Monday, naming the detainee as Benjamin Briere.

The man, whose detention since May 2020 in Iran has been confirmed by Paris, also faces charges of spreading "propaganda against the system" of the Islamic republic, wrote Dehghan.

French media have reported Briere, aged 35, was a tourist travelling in a camper van who was arrested in a desert area near Iran's border with Turkmenistan.

Le Figaro daily has reported, without giving further details, an arrest "in the desert while [the person arrested was] using a drone".

"Benjamin Briere's defence plea for the two counts of espionage and propaganda against the system has taken place," wrote Dehghan. 

"Charge of espionage [for] photographs of prohibited areas by this French tourist," the lawyer added in telegraphic style.

Dehghan -- who represents the Franco-Iranian researcher Fariba Adelkhah, currently under house arrest in Tehran -- could not immediately be reached for comment.

His tweet was accompanied by a photo of a young bearded man in an arid mountainous area, and another showing what appeared to be the same man jumping next to a motor home parked on a salt lake.

Briere was accused of "propaganda" for having asked online "why the Islamic veil is 'mandatory' in the Islamic Republic but 'optional' in other Muslim countries," wrote Dehghan.

The young man was being held at the end of February in Vakilabad prison in Mashhad, Iran's second largest city, in Iran's northeast, according to Le Point weekly. 

Prisoner exchanges

Arrests of foreigners in Iran -- especially dual nationals, who are often accused of espionage -- have multiplied since former US president Donald Trump in 2018 unilaterally withdrew the United States from the Iran nuclear deal and reimposed harsh sanctions against Tehran. 

In recent months Iran has conducted several exchanges of foreign prisoners, including researchers, with countries holding Iranian nationals. 

Adelkhah, a specialist in Shiism and post-revolutionary Iran at Sciences Po university in Paris, was arrested in early June 2019 and sentenced to five years in prison on charges of "colluding to undermine national security" and "propaganda against the system".

The researcher, who denies all the charges, left Evin prison near the capital on October 3. She has been under house arrest in Tehran since then, wearing an electronic bracelet. 

Another French researcher, Roland Marchal, who was arrested at the same time as Adelkhah, was released in March 2020, in an apparent exchange for an Iranian who was detained in France and whose extradition had been requested by the United States, according to Tehran.

According to various observers, the fate of both Briere and Adelkhah could be linked to that of Assadollah Assadi, an Iranian diplomat who was sentenced last month by a Belgian court to 20 years in prison for having planned an attack on a gathering of an Iranian opposition group in France. 

The Belgian judiciary announced on March 8 that Assadi had appealed his conviction.