There was no political motive behind the arrest of Pavel Durov, the Russian-born founder of messaging app Telegram, according to French President Emmanuel Macron.
Mr Macron's statement on X amounted to the first official confirmation of Mr Durov's arrest, nearly two days since he was detained at Le Bourget airport outside Paris shortly after landing on a private jet from Azerbaijan.
The lack of official confirmation had led to speculation about the reasons behind his detention.
Mr Macron said he had read "false information here regarding France following the arrest of Pavel Durov," adding France was deeply committed to free speech.
"The arrest of the Telegram president on French territory took place as part of an ongoing judicial investigation," he wrote. "This is in no way a political decision. It is up to the judges to decide."
A police spokesman told Reuters that Mr Durov is under investigation by the national cyber crime and fraud offices for failing to cooperate over cyber and financial crimes on Telegram, a popular messaging and social media app akin to WhatsApp. He is still in custody, the spokesman said.
Reuters was unable to speak to any lawyer representing him.
Mr Durov's arrest prompted criticism from X owner Elon Musk, who said that free speech in Europe was under attack, and calls from Russia for French authorities to accord Mr Durov his rights.
Tensions between France and Russia have been mounting for months, with French authorities accusing Russia of trying to destabilise it ahead of the Paris Olympics in response to its more hawkish stance on the Ukraine war - claims Russia denies.
Mr Durov, a 39-year-old billionaire cast as "Russia's Mark Zuckerberg" has dual French and United Arab Emirates citizenship.
Estimated by Forbes to have a fortune of $15.5billion, he said in April that some governments had sought to pressure him, but the app should remain a neutral platform and not a "player in geopolitics".
"Telegram's CEO Pavel Durov has nothing to hide and travels frequently in Europe," Telegram said in a statement. "It is absurd to claim that a platform or its owner are responsible for abuse of that platform."
When asked about his arrest, the Russian government said ithad yet to see any official French accusations against Mr Durov.
"We do not yet know what exactly Durov is accused of," Kremlin spokesman Dmitry Peskov told a news briefing.
"With what exactly are they trying to incriminate Durov? Without (knowing), it would probably be wrong to make any statements," he said.
The Russian embassy in Paris said on X that French authorities had declined to cooperate with its requests for consular access, but said it was in contact with Mr Durov's lawyer.
The embassy did not respond to a request for comment.
Telegram influential in eastern Europe
Telegram was founded by Mr Durov, who left Russia in 2014 after he refused to comply with demands to shut down opposition communities on his VK social media platform, which he has sold.
The encrypted application, with close to 1 billion users, is particularly influential in Russia, Ukraine and the republics of the former Soviet Union.
Mr Durov, who was born in Soviet Leningrad and graduated from St Petersburg State University, lists his political views as "libertarian".
He obtained his French passport in 2021 through a special procedure for high-profile foreigners exempting them from the usual legal requirements, including having lived in the country for at least five years.
The French foreign ministry, which is in charge of the procedure, did not immediately reply to a Reuters request for comment. The Elysee presidential office also declined to comment, deferring to the foreign ministry.
According to French law, any foreigner can be handed citizenship under the special rules provided he speaks French and "contributes through his outstanding work to France's influence and the prosperity of its international economic relations".
Mr Durov never lived in France and it was unclear what special link he had to the country. On 10 June, Mr Durov posted in his Telegram channel: "As a French citizen, I agree that France is the best holiday destination."
His naturalisation procedure is rare, with only 10-20 cases processed each year and each one requiring high-level political support, local media have reported.
Evan Spiegel, the founder of Snap, the maker of the Snapchat app, received French citizenship in 2018 under the same programme, local media reported at the time. Snap did not respond to request for comment.
Russian state media reported that Mr Durov also had the citizenships of Russia and of St Kitts and Nevis. Reuters was unable to verify those reports.
