French investigative judges are due to decide 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, Paralel.Az reports citing Reuters.

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 fuelled debate on where freedom of speech ends and enforcement of the law begins.

The judges' decision is expected by 8.00 p.m.(1800 GMT), 96 hours - or four days - after Durov was taken into custody, the maximum period he can be detained before they decide whether or not to put him under formal investigation.

Politico wrote that French authorities have also issued an arrest warrant for Durov's brother Nikolai, a Telegram co-founder and that the warrants targeting both brothers were issued in March.

Asked about that report, the Paris prosecutor's office said it does not comment on arrest warrants because they are covered by the secrecy of the investigation. At this stage, the only person being questioned in this case is Pavel Durov, it said.

Durov's arrest has also put in focus the uneasy relationship between Telegram, which has close to 1 billion users, and governments.

Being placed under formal investigation in France does not imply guilt or necessarily lead to trial, but indicates 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.

If Durov, who has been in police custody since his arrest, is placed under formal investigation, judges will also decide whether to put him into 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.