Telegram CEO Pavel Durov was granted bail Wednesday by a French judge under certain conditions after being put under formal investigation following a probe into organised crime on the messaging application.

The conditions require the entrepreneur to pay €5 million, report to police twice a week and to stay within the French territory, according to Reuters.

Paris prosecutor Laure Beccuau, in a statement, highlighted that the judge found substantial grounds to investigate the 39-year-old tech entrepreneur on multiple charges for which he was initially arrested four days ago.

These charges include suspected complicity in running an online platform that allows illicit transactions, images of child sex abuse, drug trafficking and fraud.

Additionally, Durov is accused of failing to cooperate with authorities, money laundering, and providing cryptographic services to criminals.

Durov's lawyer did not immediately respond to a request for comment.

Being placed under formal investigation in France does not imply guilt or necessarily lead to trial, but indicates judges consider there is enough evidence to proceed with the probe. Investigations can last years before being sent to trial or shelved.

The judge's decision came after Russian-born Durov was arrested at an airport near Paris on Saturday evening.

Durov's detention has fuelled debate on where freedom of speech ends and enforcement of the law begins. It also underlines the uneasy relationship between governments and Telegram, which has close to 1 billion users, while serving as a warning shot to tech titans who refuse to comply with authorities over alleged illegality on their platforms.

Beccuau said Telegram had been used in various criminal cases, and that the "almost total lack of response from Telegram to judicial requisitions" eventually caught the attention of the Paris prosecutor's office cybercrime unit.

"Other French investigation services and public prosecutors' offices as well as various partners within Eurojust, in particular Belgian ones, shared the same observation," about Telegram's lack of compliance, Beccuau said.

That prompted the Paris prosecutor's organised crime office to open a probe "into the possible criminal liability of the managers of this messaging service in the commission of these offences," she said in her statement.

The probe began in February, with the investigations carried out by the National Office for Minors, with an introductory indictment in July, Beccuau said.

Telegram has barely commented on Durov's arrest.

In a statement on Monday, it said it abided by European Union laws and its moderation was "within industry standards and constantly improving."

"Telegram's CEO Pavel Durov has nothing to hide and travels frequently in Europe," it said. "It is absurd to claim that a platform, or its owner, are responsible for abuse of that platform."