Pavel Durov, the Russian-born billionaire founder and owner of the Telegram messaging app, was arrested at Le Bourget airport outside Paris shortly after landing on a private jet late on Saturday and placed in custody, a police source said.

The arrest of the 39-year-old technology billionaire prompted on Sunday a warning from Moscow to Paris that he should be accorded his rights and criticism from X owner Elon Musk who said that free speech in Europe was under attack.

There was no official confirmation from France of the arrest, which French and Russian media have also reported, saying that Durov was arrested shortly after arriving at Le Bourget airport on a private jet from Azerbaijan.

France's BFM and TF1 said that Durov, who has dual French and United Arab Emirates citizenship, was arrested as part of a preliminary police investigation into allowing possible criminality due to a lack of moderators on Telegram and a lack of cooperation with police. Reuters' police source could not confirm that.

Telegram and senior Telegram managers did not respond to repeated requests for comment. The French Interior Ministry, police and Paris prosecutor's office had no comment. Durov faces possible indictment on Sunday, according to French media.

Telegram, based in Dubai, was founded by 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 one billion users, is particularly influential in Russia, Ukraine and the republics of the former Soviet Union. It is ranked as one of the major social media platforms after Facebook, YouTube, WhatsApp, Instagram, TikTok and WeChat.

Durov, who is estimated by Forbes to have a fortune of $15.5 billion, said in April some governments had sought to pressure him but the app should remain a "neutral platform" and not a "player in geopolitics."

Durov came up with the idea of an encrypted messaging app as a way to communicate while he was under pressure in Russia. His younger brother, Nikolai, designed the encryption.

"I would rather be free than to take orders from anyone," Durov said in April about his exit from Russia and search for a home for his company which included stints in Berlin, London, Singapore and San Francisco.

After Russia launched its invasion of Ukraine in 2022, Telegram has become the main source of unfiltered - and sometimes graphic and misleading - content from both sides about the war and the politics surrounding the conflict.

The platform has become what some analysts call 'a virtual battlefield' for the war, used heavily by Ukraine's President Volodymyr Zelenskiy and his officials, as well as the Russian government.

Russia's foreign ministry said it had sent a note to Paris demanding access to Durov, although it said that he had French citizenship.

Former Russian President Dmitry Medvedev said that Durov had misjudged by fleeing Russia and thinking that he would never have to cooperate with the security services abroad.

Medvedev, who regularly uses Telegram to criticize and insult the West, said Durov wanted to be a "brilliant 'man of the world' who lives wonderfully without a Motherland."

"He miscalculated," Medvedev said. "For all our common enemies now, he is Russian – and therefore unpredictable and dangerous."

Russia began blocking Telegram in 2018 after the app refused to comply with a court order to grant state security services access to its users' encrypted messages.

The action interrupted many third-party services, but had little effect on the availability of Telegram there. The ban order, however, sparked mass protests in Moscow and criticism from NGOs.

Dubai-based Durov had been travelling from Azerbaijan and was arrested at around 8 p.m. (1800 GMT), according to French and Russian media.

Telegram says it "is committed to protecting user privacy and human rights such as freedom of speech and assembly."

Durov has previously accused U.S. law enforcement agencies such as the Federal Bureau of Investigation (FBI) of seeking to get a backdoor into the platform. The FBI has not commented on those allegations.

Telegram's increasing popularity, however, has prompted scrutiny from several countries in Europe, including France, on security and data breach concerns.

Musk, billionaire owner of X, the social media platform formerly known as Twitter, said after reports of Durov's detention: "It's 2030 in Europe and you're being executed for liking a meme."

Outside the French embassy in Moscow, a lone protester held up a sign reading: "Liberté pour Pavel Durov."