PARIS—French authorities detained Pavel Durov, the founder and chief executive of the Telegram messaging app, as part of a broad investigation into online criminality opened last month, the Paris prosecutor’s office said Monday, raising the stakes in the struggle between governments and digital companies over their responsibility for illegal activity on their platforms.

The investigation is examining 12 potential criminal violations, including complicity in the spread of child pornography, refusal to cooperate with authorities and complicity in fraud. Investigators haven’t named Durov or anyone else yet as the target of their probe, according to the statement. The prosecutors said they have 96 hours, or until Wednesday, to hold Durov for questioning.

France’s decision to detain the 39-year-old tech entrepreneur is a sign of the growing concern among governments, particularly in Europe, about Telegram and other platforms being used to sow unrest and fuel criminal activity. Those concerns range from posts that authorities say fuel antisemitism and racism to the exchange of illegal content or goods such as child pornography or counterfeit merchandise. Durov’s detention, however, generated criticism on X, the social-media platform owned by Elon Musk, who posted “#FreePavel” and said France was attempting to censor Telegram.

French President Emmanuel Macron on Monday took the unusual step of publicly defending the judicial investigation, a sign of the sensitivity surrounding the decision to detain Durov. French leaders rarely comment on judicial proceedings to avoid compromising the independence of judges and prosecutors.

“I read false information here about France following the arrest of Pavel Durov,” Macron said Monday in a post on X. “The arrest of the president of Telegram on French soil took place as part of an ongoing judicial investigation. It is in no way a political decision. It is up to the judges to rule on the matter.”

Police took Durov into custody at Le Bourget airport north of Paris on Saturday night when his private jet landed after a flight from Baku, the capital of Azerbaijan.

Durov

French President Emmanuel Macron said Monday that the arrest ‘is in no way a political decision.’ A file photo shows the French president delivering a speech during a ceremony commemorating the 80th anniversary of the Liberation of Paris next to the Denfert Rochereau Square in Paris, France, August 25, 2024. Teresa Suarez/Pool via REUTERS

France’s judiciary is one of the country’s most powerful institutions, and its judges and prosecutors are fiercely independent. They have investigated some of the country’s most powerful political figures, including the current justice minister, Éric Dupond-Moretti; judicial authorities ultimately declined to send him to trial. For years, judges have investigated former President Nicolas Sarkozy for a series of possible crimes. A court convicted him this year of violating campaign-finance laws.

French law requires social-media companies and other online platforms to cooperate with authorities in countering the spread of illegal content. It is mirrored to some extent by the Digital Services Act, the European Union law requiring platforms to prevent such content.

Telegram said it complies with EU law, while also saying it was “absurd” to hold a platform responsible for those who abuse it.

“In a state governed by the rule of law, freedoms are upheld within a legal framework, both on social media and in real life, to protect citizens and respect their fundamental rights,” Macron said.

Kremlin spokesman Dmitry Peskov told reporters Monday that Moscow doesn’t know why Durov was detained or what he is accused of. Peskov urged against drawing any conclusions until Durov is charged, “if he is charged at all.”

Telegram is the most important social-media and chat app in post-Soviet nations, and it has an estimated 900 million users worldwide. The company said in February that it has 41 million active monthly users inside the EU, putting it just under the threshold for heightened monitoring and enforcement under the EU’s Digital Services Act.

Durov’s company, which he relocated to Dubai in 2017, has become a central information source about Russia’s war with Ukraine. Government authorities in Russia and Ukraine use Telegram to push news and information about the war, as do liberal opposition groups inside and outside Russia. Moscow has also used it to recruit agents in Europe for acts of sabotage and operations aimed at sowing unrest.

That would potentially make Durov a valuable asset for Western intelligence agencies seeking to crack open Telegram’s encrypted communications. France has been a target of several Russian operations in recent months, French officials say, drawing complaints from Macron and others in the government. In an interview this year with the former Fox News host Tucker Carlson, Durov said that during his latest trip to the U.S., officials approached an engineer traveling with Durov and tried to pay the engineer to insert code into the Telegram platform; Durov said that code would allow spy agencies to snoop on users’ communications.

Durov’s app has occupied an increasingly important place in the Russian media landscape, because it has largely escaped the Kremlin’s crackdown on other media platforms and publications since Russia’s invasion of Ukraine in February 2022. There has been limited censorship of images uploaded to the app, including video of Russia’s military bombing civilian areas in Ukraine and Kyiv’s forces capturing Moscow’s troops.

Ann M. Simmons contributed to this article.