Tehran's prosecutor has filed criminal charges against the "management" of encrypted messaging app Telegram, referring to allegations that the cloud-based service, hugely popular in Iran, serves as a platform for child pornography and extremist content, Iranian news agencies reported on September 27.

Telegram - founded in 2013 by the charismatic Russian internet entrepreneur Pavel Durov, who is currently battling a demand from Russia's main security agency for the encryption keys to his service - is the choice of many millions of Iranians for social media messaging and exchanging news and information. For many voters, for instance, it took a prominent role in the May presidential election. Durov has claimed as many as 40 million active users of his service in Iran, a country of 80 million people. They include prominent politicians and media outlets.

Prosecutor Abbas Jafari Dolatabadi claimed that even Islamic State militants had been posting content on the app in Iran, the semiofficial ISNA news agency and Mizan news agency, which reports on the judiciary, both reported.

Reacting on Twitter, Durov said he was surprised to learn of the reported charges and added that he believed the "real reasons [for the charges] are different" than child pornography and extremism. "We are actively blocking terrorist and pornographic content in Iran," Durov asserted on Twitter.

In March, Iranian authorities arrested 12 managers of Telegram channels seen as reformist and anti-hardliner. Critics claimed it was a crackdown ahead of the presidential election in which the hardliners tried, but badly failed, to stop the re-election of centrist and pragmatist President Hassan Rouhani. The president criticised the arrests.

Iran’s censors - some of the world's toughest - monitor tens of thousands of websites, including social media and news sites, for content they see as too sensitive or immoral.

The Telegram case is being handled by the international affairs department of the Tehran prosecutor's office.

Telegram is registered as both an English LLP and an American LLC. The service says that it is headquartered in Berlin, but it does not disclose exactly where it rents offices or which legal entities it uses to agree rental contracts. The Telegram team needs "sheltering from unnecessary influence" and users require protection from governmental data requests, the company says.

Durov also founded Russian-based online social media and networking service VK (VKontakte, or “InContact”). After being dismissed from his post as VK’s CEO in 2014, he, and his older brother Nikolai Durov, left Russia to go into self-imposed exile. They are said to be moving from country to country with a small group of computer programmers.