The Islamic State and other terror groups are flocking to a Berlin-based social-media service that imposes few barriers on the distribution of violent content or recruiting propaganda, according to a new report.

Thousands of followers have subscribed to Islamic State-related channels on the social-media platform called Telegram in recent weeks, according to the Middle East Media Research Institute, a Washington-based organization that tracks online activities of terrorist groups.

Founded by a high-profile Russian programmer who fled that country last year, Telegram is designed to protect users' anonymity. Unlike Twitter, Facebook and other established platforms, Telegram has no clear mechanism for law enforcement agencies to track individuals or demand that material aimed at inciting terror attacks be taken down.

"Telegram's channels offer no way in to monitor them," the report concludes. Citing the "large number of members" that Islamic State channels are drawing, the report said, Telegram is poised "to become a fertile and secure arena for jihad-related activities."

Telegram, which is a nonprofit organization, did not respond to requests for comment.

The emergence of Telegram has complicated efforts by the FBI and other agencies to monitor or counter the surging volume of online propaganda from terror groups. The service is still relatively small in scale, but offers an alternative to Twitter, Facebook and other companies that police content more aggressively under pressure from the U.S. government.

Telegram was conceived as an encrypted communications tool but last month unveiled a new service enabling users to create "channels" that can disseminate images, videos and other material to thousands of anonymous subscribers.

A channel affiliated with the Islamic State supporters called "Nasher" has attracted more than 10,000 members and distributes propaganda in languages including Arabic, English, French and German, according to the report by the research institute, also known as MEMRI.

"The whole notion [for Telegram users] is 'we have a platform that we can use to attract followers and publish our stuff without anyone really stopping us,' " said M. Khayat, the principal author of the study, who asked to be identified by his first initial out of security concerns.

Another new channel is devoted to encouraging attacks in Saudi Arabia. Users have posted "repeated calls to carry out lone wolf attacks there" and distributed information on how to train and acquire weapons, according to the report. So far, the channel has only 51 subscribers.

Experts said that Telegram is unlikely to supplant more mainstream social-media sites because of their global reach and massive user bases.

"Telegram, while it has a growing usage, is not anything on the same scale as Twitter," said Charlie Winter, a senior researcher at the Quilliam Foundation, a research organization in the United Kingdom. Islamist groups "will still need to use Twitter and sites like that to bring new supporters and sympathizers into the echo chamber. But perhaps we can see Telegram become the hub for initial propaganda dissemination."

Telegram has gained favor among militants in part because it has not banned the distribution of violent or gruesome images the way that Twitter and Facebook have or created a mechanism for users to report violations of the organization's terms of service, experts said.

Khayat said that he had contacted Telegram to ask about these policies and that the organization responded by saying that its channels are the "private territory of their respective participants and we do not process any requests related to them."

Winter said he had recently seen an online posting from an Islamic State follower, declaring that "Twitter can suspend me 1,000 times but I will always be on Telegram."

The service was created by Pavel Durov, who has been called Russia's Mark Zuckerberg because of his role in founding the social-networking site VKontakte, which is more popular in that country than Facebook.

Durov, 31, gained attention by offering a job to Edward Snowden when the former U.S. intelligence contractor was granted asylum in Russia after exposing massive U.S. eavesdropping operations overseas.

But Durov fled Russia himself last year after refusing to comply with Moscow's demands that he turn over account information on Ukrainian protesters. Durov engaged in a stand-off at his St. Petersburg home with a Russian SWAT team, and control of his company was subsequently seized by allies of President Vladimir Putin.

In an interview with The New York Times last year, Durov said he is "not a big fan of the idea of countries," and that he had created Telegram to offer better privacy and security than other platforms.

Telegram also enables users to message one another directly through encrypted exchanges, a capability that is particularly worrisome to law enforcement agencies. Islamic State operatives have used similar tools to encourage supporters to travel to Syria or carry out attacks.

FBI Director James Comey warned last year that law enforcement agencies were at risk of "going dark" because of expanding encryption capabilities. The FBI declined to comment on the Islamic State's use of Telegram.