Telegram in a statement defended its operations, saying it abides by European Union laws and its content moderation is “within industry standards and constantly improving”.
Durov, the company added, had “nothing to hide and travels frequently in Europe”.
French media reports that Durov was detained on an arrest warrant alleging his messaging platform had been used for money laundering, drug trafficking and other offences.
A French investigative judge extended Durov’s detention order on Sunday night, French media reported, but he had not been charged and few details were available on the investigation.
A statement from the Paris prosecutor’s office said Durov’s police custody order was extended on Monday evening for up to 48 hours.
Under French law, Durov can remain in custody for questioning for up to four days. After that, judges must decide to either charge or release him.