Telegram's founder, Pavel Durov, is now under formal investigation in France as part of an inquiry into organized crime activities on the messaging app, according to Paris prosecutors.
Durov, 39, has not been taken into custody but is under judicial supervision and must pay a deposit of €5m (£4.2m; $5.6m).
The Russian-born billionaire, who holds French citizenship, is required to report to a French police station twice a week and is prohibited from leaving the country.
Durov was initially detained after landing at Le Bourget airport near Paris last Saturday, under a warrant for app-related offenses.
On Wednesday, Paris prosecutors stated that Durov was formally investigated for several alleged offenses, including complicity in managing an online platform for illicit transactions by an organized gang, refusal to cooperate with authorities, and complicity in the organized criminal distribution of child sexual images.
In France, being placed under formal investigation does not imply guilt or guarantee a trial, but it signifies that judges believe there is enough evidence to warrant an investigation.
Durov has not commented publicly on the situation.
His lawyer, David-Olivier Kaminski, emphasized that Telegram adheres to European digital regulations and is moderated similarly to other social media platforms.
He called it "absurd" to claim that his client was involved "in criminal acts that don't concern him either directly or indirectly."
This marks the first time the owner of a social media platform has been arrested due to the platform's usage, sparking a heated debate online about freedom of speech and responsibility.
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