PARIS - French investigative judges are due to decide later on Wednesday whether to place Russian-born Telegram boss Pavel Durov under formal investigation following his arrest as part of a probe into organised crime on the messaging app.

Durov's detention as he landed at an airport near Paris on a private jet on Saturday evening has put the spotlight on the criminal liability of app providers and also triggered debate on where freedom of speech ends and enforcement of the law begins.

With close to 1 billion users, Telegram is particularly prominent in Russia, Ukraine and the republics of the former Soviet Union.

Being placed under formal investigation in France does not imply guilt or necessarily lead to trial. But it shows that judges consider there is enough to the case to proceed with the probe. Investigations can last years before being sent to trial or shelved.

Should Durov, who has been in police custody since his arrest, be placed under formal investigation, judges will also decide whether to put him in pretrial detention. One of the factors they will consider is whether he could try to flee.

A source at the Paris prosecutor's office said an update on the probe was likely to be issued late on Wednesday.

The overall investigation is at this stage directed against unspecified people.

It focuses on suspected complicity in crimes including running an online platform that allows illicit transactions; possessing images of child sex abuse; drug trafficking; fraud; refusing to pass information to authorities; and providing cryptographic services to criminals, prosecutors said.

The prosecutor's office did not say which crime or crimes Durov himself might be suspected of.

Durov's French lawyer did not reply to repeated Reuters requests for comment through emails and phone calls.

His arrest, which President Emmanuel Macron said was not politically motivated, has further damaged already strained diplomatic relations between Russia and France, which has supported Ukraine in its fight against Russia's invasion.

Durov was taken into custody at 8 p.m. (1800 GMT) on Saturday, and his detention can last 96 hours - or a maximum of four days - before judges decide on whether to put him under formal investigation or not.

  - Reuters