That has helped push some of Telegram’s Russian-language news, politics and commentary channels—already among the app’s most popular—to double and triple their numbers of subscribers in recent weeks, with several gaining more than a million new followers in a matter of days.

Telegram’s growth comes as Russian President

Vladimir Putin

is lowering a digital iron curtain on the country, which has been targeted by sweeping Western sanctions. Several channels with large followings carry posts that appear to defy the Kremlin’s decision to criminalize what it considers to be false information about the conflict, such as describing it as a “war” or “invasion.”

One Russian-language channel run by independent journalist Ilya Varlamov, which offers a stream of news updates that have included footage of burning apartment buildings in Kyiv, increased its subscriber-count fivefold to nearly 1.3 million since the war began, according to statistics service Telemetrio. Earlier this week, the channel shared uncensored video footage of the moment when an employee of Russian state-television Channel One ran on its evening news broadcast with a poster that read “Don’t believe the propaganda” while shouting “Stop the war.” It was viewed 1.2 million times.

The freewheeling nature of Telegram has experts guessing how the app has survived the Kremlin’s cull of other social-media platforms. Some analysts say the app’s following in Russia makes it too big to cancel.

For years, Telegram, which was initially started in Russia, has been the go-to news feed for many people in the country. It has become a major outlet for the Kremlin’s own message, both through proxies and official government accounts. Many pro-Kremlin channels on Telegram are growing as fast, if not faster, than independent or pro-Ukraine ones. Russian state-owned news service RIA Novosti has increased its number of Telegram subscribers nearly fourfold to 1.6 million since the war began, Telemetrio data show.

“Telegram isn’t perceived as a total enemy resource. It’s not perceived as a tool of information war against Russia,” said Ivan Kolpakov, editor in chief and co-founder of Meduza, a Russian-language independent publication whose website was blocked by the Kremlin but which remains available on platforms including Telegram. “In Russia, a huge culture of uncensored journalism and so-called journalism appears on Telegram,” he added.

A Telegram spokesman said the company doesn’t know why Russian regulators haven’t blocked the application, or whether they will attempt to do so. He said that Telegram has seen “a notable influx of users from Russia and Ukraine,” adding: “We believe in freedom of speech and are proud we can serve people in different countries in difficult times.”

Both the

New York Times

and Washington Post have in recent days started using Telegram channels to publish some of their reporting on the war in Ukraine.

Telegram was founded in 2013 in Russia by Pavel Durov and his brother just months before Mr. Durov was ousted from VK, a Russian social-media platform that is similar to Facebook. Mr. Durov, now based in Dubai, has long taken a libertarian viewpoint on content moderation, saying his app, which allows users to encrypt specific chats, puts a priority on privacy, security and free speech.

On his Russian-language public channel, Mr. Durov said on Feb. 27 that he would consider restricting channels in Russia and Ukraine during the war to rein in unverified information, before reversing course, citing appeals from users.

“I ask you to double-check and not take on faith the data that is published in Telegram channels during this difficult period,” he added.

Telegram introduced public-facing channels on top of its private messages in late 2015, turning it into a social media platform—quickly leading to tensions with governments. The app faced criticism in Europe when Islamic State used its channels as a recruitment tool, and to help incite followers to commit a spate of terrorist attacks.

The company has added more content moderation and bans pornography and explicit calls for violence under its terms of service. Telegram says it removes tens of thousands of terrorist bots and channels every month, including 19,000 in February. The company also more recently complied with European Union sanctions orders to prevent accounts in the EU from viewing Telegram channels for Russian state-owned media outlets RT, formerly known as Russia Today, and Sputnik News.

In Russia, Telegram racked up 50 million rubles in fines over the course of 2021, equivalent to around $483,000 at today’s exchange rate, for failing to remove banned content, the Telegram spokesman said. The app didn’t remove any channels or automated accounts when Russia’s telecommunications watchdog in March asked it to remove a set of automated accounts offering information about captured or killed Russian soldiers, the spokesman added.

“Any requests related to political censorship or limiting human rights such as the rights to free speech or assembly are not and will not be considered,” the Telegram spokesman said.

Some digital-media experts say Russia might be tolerating Telegram’s noncompliance in part to avoid a popular backlash. Telegram says that 7% to 8% of its users are in Russia, which works out to more than 40 million people. Banning it risks driving people in Russia to explore using virtual private networks, anticensorship browser extensions and other tools to skirt past the online blockade, the experts say. That is what happened when Iran tried to block Telegram beginning in late 2017.

Another explanation may be that blocking Telegram might be technically difficult for Russia, internet experts say. The country attempted to block Telegram for more than two years beginning in 2018, citing its refusal to turn over account information in terrorism investigations. But despite regulators banning what Telegram described as thousands of IP addresses a day, the app continued to thrive in Russia.

“Telegram is able to do things that make it extremely difficult to knock it offline,” said Ethan Zuckerman, a professor of public policy, communication and information at the University of Massachusetts at Amherst.

In June 2020, the Russian regulators lifted the block. Critics of Telegram questioned whether the app struck a deal behind the scenes with the Kremlin. But the company said that the decision was solely Russia’s. The regulator didn’t respond to an emailed request for comment on why it lifted the ban, but said at the time that it had done so because of Telegram’s stated willingness to counter terrorism on its platform.

“We have a consistent history of ‘zero compromise’ when facing bans in countries like Iran, China or Russia,” the Telegram spokesman said. “We didn’t negotiate with Russia in 2018 when we still thought their ban of Telegram might be successful, let alone in 2020 when it turned out their ban was ineffective,” he added.

Moving to block Telegram now would also risk disrupting the communications of some of the Kremlin’s biggest backers. The Telegram feed of

Ramzan Kadyrov,

leader of the Chechen Republic and an ally of Mr. Putin, has become one of the platform’s fastest-growing Russian-language channels, publishing a stream of pro-Kremlin bravado and taunting to 1.1 million subscribers, a group that has grown 20-fold since before the invasion, Telemetrio data show.

Tesla

and SpaceX founder

Elon Musk

who had quipped last week on Twitter that he would challenge Mr. Putin to a fight. “Vladimir Vladimirovich will look unsportsmanlike when he beats a weaker opponent,” Mr. Kadyrov responded in Russian on Telegram, using Mr. Putin’s patronymic and saying Mr. Musk should first train for the fight in Chechnya.

In a follow-up post on Twitter, Mr. Musk declined the offer, but said he was willing to fight Mr. Putin with his left hand.

—Evan Gershkovich contributed to this article.

Write to Sam Schechner at sam.schechner@wsj.com