Pavel Durov, billionaire founder and CEO of the Telegram messaging app, was arrested at the Bourget airport outside Paris on Saturday evening, TF1 TV and BFM TV said, citing unnamed sources.

Telegram, particularly influential in Russia, Ukraine and the republics of the former Soviet Union, is ranked as one of the major social media platforms after Facebook, YouTube, WhatsApp, Instagram, TikTok and Wechat. It aims to hit one billion users in the next year.

Based in Dubai, Telegram was founded by Russian-born Durov. He left Russia in 2014 after refusing to comply with government demands to shut down opposition communities on his VK social media platform, which he sold.

Durov was travelling aboard his private jet, TF1 said on its website, adding he had been targeted by an arrest warrant in France as part of a preliminary police investigation.

TF1 and BFM both said the investigation was focused on a lack of moderators on Telegram, and that police considered that this situation allowed criminal activity to go on undeterred on the messaging app. Telegram did not immediately respond to a Reuters request for comment. The French Interior Ministry and police had no comment.

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 app has become preferred means of communications for Ukraine’s President Volodymyr Zelenskiy and his officials. The Kremlin and the Russian government also use it to disseminate their news. It has also become one of the few places where Russians can access news about the war.