Born in 1985, Briere was arrested when flying a drone and taking photographs in a “prohibited area”.
His lawyer Saeid Dehqan says investigation had been completed and the prosecution had confirmed the charges.
“The prosecutor is preparing the indictment and sending it to the revolutionary court for the continuation of the judicial process,” Dehqan told AFP.
Currently jailed in the city of Mashhad in northeastern Iran, Briere was also facing charges of “corruption on earth”, one of the most serious offences under Iranian law, and drinking alcohol, punishable by flogging, but those charges were dismissed after the investigation.
The announcement comes days after an open letter from Briere’s sister, Blandine Briere, was published by French weekly Le Point, in which she appealed to French President Emmanuel Macron to push for her brother’s release.
She said the charges were “baseless” and that Briere had become a “negotiating tool”.
In March, a spokesman for the French foreign ministry said Briere was benefitting from consular support and that its embassy in Tehran was in “regular contact” with him.