In that climate, Telegram -- which was itself blocked for a period by the Kremlin for refusing to cooperate with Russian law enforcement agencies -- has become one of the last bastions of free speech and uncensored information.
Moscow now fears for the fate of the messenger and its Russian-born founder Durov, charged late August with failing to curb extremist and illegal content on the platform.
Though he has been released on bail, he cannot leave the country and the Kremlin has warned France against turning the case against him "into political persecution."
Durov's arrest is not the only headache the privately-owned service faces.
The European Commission is also investigating whether Telegram has more EU users than claimed and must therefore comply with more stringent rules.
'For all Russians'
In Russia, Telegram channels widely cover subjects that are otherwise strictly censored in state media.
That includes everything from front-line reports of the conflict in Ukraine to trials of Kremlin critics and manifestos dispatched from political prisoners.
The most popular channels have millions of subscribers.
The Kremlin, government ministries and regional governors also use Telegram as their go-to public communications tool.
"Telegram is a very practical and reliable messaging service for all Russians, regardless of their political opinions," said Alexei Venediktov, head of the Echo of Moscow radio station, blocked in Russia after its criticism of the Ukraine offensive.
The messaging service "is considered independent of the Russian state," the veteran journalist -- who has over 200,000 subscribers there -- told AFP.
Blocking Telegram would be equivalent to "a measure of censorship," he said.
'Main source of information'
Telegram's popularity has grown steadily in Russia throughout the Ukraine conflict, after Russia blocked access to Instagram, Facebook and X, as well as the websites of several opposition media outlets.
It is the fourth most popular online service, ahead of YouTube and the Russian social network VKontakte, according to a study by Russian media research group Mediascope.
It is also heavily focused on news. Two-thirds of its Russian readers prefer to follow political and news channels, with only six percent preferring entertainment or cinema, for instance.
Mila, a 45-year-old psychologist, said she started using it after Facebook was blocked and she now subscribes to some 80 Telegram news channels. She also uses it to communicate privately with friends who are against the offensive in Ukraine.
"Today, it is my main source of information. If Telegram stops working, it will hurt me a lot," Mila told AFP, speaking on condition her full name not be used.
Naida, a 56-year-old logistician said she trusts Telegram more than other messaging services.
"And all the news is there, you don't need to have a VPN on all the time," she said.
Telegram is now "the main source of information" for those seeking independent views, said political scientist Tatiana Stanovaya of the Carnegie Russia Eurasia Center.
"Telegram has no alternative" in Russia, she said, adding the free flow of information on the service is a throwback to before President Vladimir Putin began to crack down hard on dissent.
Battlefield communications
Amid the conflict in Ukraine, the platform has also become a key military communication tool.
Both Russia and Ukraine warn their populations of incoming air attacks via Telegram posts, while their armies use it to communicate and coordinate internally.
"Telegram has almost become the main way of commanding units on both sides of the front," said Mikhail Zvinchuk, a former military officer whose Telegram blog on the conflict, Rybar, has more than 1.3 million subscribers.
Pro-Kremlin Russian journalist Andrei Medvedev also said Telegram was "the main messaging service" of the conflict.
"It is an alternative to the secret military communication system," he said.
Thanks to its broad appeal across the political spectrum, the fate of Durov and the implications for the site have become a rare point of unifying concern.
Russian opposition politician Ilya Yashin, recently released as part of a historic prisoner exchange with the West, is among those who have taken Durov's side.
"I do not consider Pavel Durov a criminal, and I hope that he will be able to prove his innocence," Yashin said.
