Pavel Durov, the Russian-born entrepreneur who founded the Telegram messaging platform, was arrested on Saturday in France, as part of an investigation by French prosecutors into criminal activities on the app.

Some supporters of Telegram have denounced the arrest as an example of government censorship. The platform’s growth has been fueled partly by its hands-off approach to content moderation, making it an important means of communication but also a haven for harmful content.

Here’s what we know about Mr. Durov’s arrest and what happens next.

Pavel Durov was detained on Saturday near Paris.

Mr. Durov was arrested at Le Bourget Airport, about five miles north of the French capital, after landing on a private plane from Azerbaijan.

He has not been charged but is currently in custody and being questioned at France’s National Anti-Fraud Office, a law enforcement agency that handles a wide range of financial crimes.

Under French law, Mr. Durov’s detention can be extended through Wednesday: After that, the authorities must charge or release him. If he is charged, prosecutors could ask a judge to keep him in custody, but he could also be released under certain conditions.

Russia and the United Arab Emirates, where Telegram is based, have requested consular access to Mr. Durov. He is a citizen of both countries and also holds a French passport.