The surprise arrest of the Russian-born co-founder of Telegram, Pavel Durov, after he stepped off his private jet in Paris last Saturday night, has brought the one-time fringe social network under the glare of the spotlight like never before.

Durov’s arrest – after an investigation by the Paris prosecutor into organised crime, child sex abuse images, fraud and money laundering on the platform – also raises the stakes for the European Union, which has adopted the world’s most ambitious laws to police the internet, notably the Digital Services Act (DSA). Coming into force in November 2022, the DSA targets online platforms “too big to care” – in the words of the EU commissioner, Thierry Breton – putting demands on internet firms to remove illegal content, protect children, tackle disinformation and other online harms.

The European Commission has kept its distance from the French investigation into Durov. “It is purely a criminal investigation at national level, carried out by the French authorities … based on French criminal law,” a spokesperson said. “It has nothing to do with the DSA.”

But the charges laid out against the 39-year-old tech billionaire increase pressure on the commission and Belgium, the member state responsible for regulating Telegram on behalf of the bloc. “If there is such a big problem with content moderation that it is actually criminally relevant … why hasn’t that been addressed under the DSA yet?” said Jan Penfrat at the European Digital Rights group (EDRi), a coalition of NGOs. “One possible answer is, of course, the DSA is new … but still it does create a kind of pressure on the authorities.”

The hybrid messaging service/social network, which has groups of users up to 200,000-strong, has worried European politicians for months. While Telegram has been favoured by pro-democracy activists in Russia, Hong Kong and Iran, it has also become a haven for extremists, criminals, conspiracy theorists and pro-Kremlin propagandists. In Lithuania, police have set up special units to monitor Telegram and other platforms in a bid to curb drug trafficking, while Dutch police told the country’s public broadcaster that it had had little cooperation from the platform after NOS journalists found 2.5m messages offering drugs on the site in 2023.

Based in the United Arab Emirates, Telegram has mushroomed to nearly a billion users worldwide while under limited regulation. But despite claiming only 41m active monthly users in the EU, it now faces new demands under European law.

Enforcement of the law could be a weak link in the chain. Belgium – along with five other EU member states – is subject to ongoing EU legal proceedings for failure to empower its “digital services coordinator”, the organisation responsible for enforcing the DSA. While the Belgian government has charged the Belgian Institute for Postal Services and Telecommunications to enforce the DSA, the agency lacks sufficient powers, meaning it is unable to launch investigations into Telegram.

Telegram, however, may come under direct purview of the EU executive. Until now it has not been subject to strictest regulation that only applies to the largest platforms, such as Meta’s Facebook and X, formerly known as Twitter. Under EU law only platforms with more than 45m monthly active users are “very large online platforms” [VLOPs] subject to the most stringent requirements, and direct supervision by the commission.

Senior EU officials are not convinced by Telegram’s claim to be just under the threshold, with 41m active monthly users in the EU. “Telegram is an issue,” Vĕra Jourová, a European Commission vice-president told Bloomberg in May. “We are now checking whether the figure is right,” she said, adding that “even the smallest platforms can do a very dangerous job in several member states”, referring to Telegram’s popularity in eastern EU countries with large Russian-speaking minorities.

The commission spokesperson said on Tuesday that it was “carefully analysing” Telegram’s figures, adding: “Once we will come to a clear conclusion, we will indeed not hesitate – if they meet the threshold – to designate Telegram [as a VLOP].”

Separate to these ongoing talks between the commission and Telegram, the platform must publish its latest monthly user data in the EU by the end of this month.

Telegram did not immediately respond to requests for comment. But after Durov’s arrest the company said it “abides by EU laws, including the Digital Services Act”.

Digital campaigners say Telegram needs to be much more transparent. “An online platform of that importance with that large user base, even if it isn’t officially designated a VLOP, is just way too important in order to operate with that level of opaqueness,” said Penfrat at EDRi.

“The public needs to know what’s going on and obviously regulators need to know in order to be able to do their job.”