PARIS (Reuters) -A French judge put Telegram boss Pavel Durov under formal investigation on Wednesday as part of a probe into organised crime on the messaging app, but he can avoid pretrial detention by making a 5 million euro bail payment, reporting twice a week to police and not leaving French territory.

The judge's decision came four days after Russian-born Durov was arrested at an airport near Paris.

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.

Durov's arrest has put the spotlight on the criminal liability of messaging app providers and fuelled debate on where freedom of speech ends and enforcement of the law begins.

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