A Frenchman will face trial in Iran after prosecutors confirmed he was charged with espionage.
Mr Briere is also charged with "propaganda against the system", which can incur a prison sentence of three months to one year.
Mr Briere's lawyer, Said Dehghan, told AFP the investigation was complete 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," he said.
It's unclear when the trial will be.
In March, Mr Dehghan wrote on Twitter that the propaganda charge related to Mr Briere questioning on social media Iran's mandatory hijab policy.
Mr Briere is being held in the city of Mashhad in north-eastern Iran. He had faced accusations of "corruption on Earth", one of the most serious offences under Iranian law, and drinking alcohol, punishable by flogging, but those charges were dismissed.
Last week, his sister Blandine Briere appealed to French President Emmanuel Macron to secure her brother's release.
In an open letter published by French magazine Le Point, she wrote that the charges were "baseless" and that Mr Briere was a "negotiating tool".
Ms Briere said her brother was a tourist who was thirsty for adventure and discovery.
In March, a spokesman for the French Foreign Ministry said Mr Briere, born in 1985, was receiving consular support and its embassy in Tehran was in "regular contact".
Arrests of foreigners in Iran – especially dual citizens who are often accused of espionage – have increased since former US president Donald Trump in 2018 withdrew from a nuclear deal with Iran and reimposed heavy sanctions on Tehran.
Iran has conducted several exchanges of foreign prisoners, including researchers, with countries holding Iranians.
In 2020 Paris and Tehran swapped French researcher Roland Marchal for Iranian engineer Jalal Ruhollahnejad
World powers, including France, have been engaged in negotiations with Iran in Vienna since April to try and revive the nuclear deal.
Iranian diplomats said during the talks that Tehran was open to exchanging prisoners.
Negotiations in the Austrian capital are in their fifth round with no plans for a sixth, Russia's envoy to the talks said.
"The negotiators proceed from the understanding that the current round should be final," Mikhail Ulyanov wrote on Twitter on Sunday.