Pavel Durov, the billionaire founder of encrypted messaging app Telegram, has been arrested in France, according to local reports.
The 39-year-old Franco-Russian tech chief had just arrived via private jet when he was arrested at Le Bourget airport in the outskirts of Paris, BFMTV reports.
Quoting an unnamed source, the outlet added he was the subject of a search warrant in France.
Telegram is one of the most downloaded apps in the world, with Mr Durov saying in July it has close to one billion users.
It offers end-to-end encryption - where data can only be accessed by the direct users - for user's calls and "secret chats," and has a focus on privacy.
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What is Telegram and why is it so popular?
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This focus makes the app popular with pro-democracy movements and other protesters in countries with strict laws, but it has also been used for criminal activity and recently by far-right activists who sparked riots in the UK over the Southport stabbings.
It is unclear what Mr Durov was arrested for: BFMTV reported the warrant concerned the app's possible use in money laundering, drug trafficking or sharing of child sex abuse content.
The app's founder, owner and chief executive left Russia in 2014 after losing control of his previous social media company VK for refusing to hand over the data of Ukrainian protesters to security agencies.
He was naturalised as French in August 2021, and is also a citizen of the United Arab Emirates.
In an interview with US commentator Tucker Carlson in April, Mr Durov said he was determined to keep Telegram "neutral" and "free from geopolitics".