Telegram encrypted messaging app has blocked more than 8,500 in October due to terrorist links and incitement of violence, Pavel Durov, the company’s CEO, said.

“The promotion of violence in any form is banned” by Telegram, Durov said on his channel on Sunday. “Only in October, we blocked more than 8,500 channels associated with terrorism,” he added, saying that the line, which shouldn’t be crossed, was “clear.”

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“One can criticize the local authorities, challenge the status quo and arrange a political debate. At the same time, one can’t encourage violence and call for actions that will harm innocent people. Here is the main criterion for moderation of our public channels,” he explained.

The tech entrepreneur said one example was a popular Iranian channel which asked its subscribers to throw stones at public facilities and film it on video. Telegram contacted its owner and demanded calls for vandalism to be removed. But instead, the channel launched a new contest for its viewers, which involved throwing Molotov cocktails at mosques, and was immediately blocked, he said.

Durov argued that he and his team have been protecting the freedom of speech for the last 11 years and are now doing it on an international level. He again referred to Iran, saying that the BBC is banned in the country, but its Telegram channel has 953,900 subscribers.

In late September, a Tehran prosecutor said that Iran pressed charges against Durov over Telegram’s popularity with terrorists, child pornographers, and other criminal elements. The encrypted app allows around 20 million Iranians to bypass the Islamic Republic’s ban on social media.

It also has a feature which lets users set their messages to “self-destruct” after they were read by the addressee. Telegram was previously blamed for being used by the terrorists and other criminals for communication purposes.

Indonesia blocked the web versions of Telegram in July, arguing that “many channels in the service are propaganda of radicalism, terrorism, hatred, invitation or how to assemble bombs.”

READ MORE: Indonesia blocks access to Telegram over ‘terrorist propaganda’ concerns

Russia’s Federal Security Service (FSB) said that the app was used by the terrorists behind the St. Petersburg Metro suicide attack which killed in 15 people in April. The agency then specifically mentioned that Telegram was popular among terrorists, taking advantage of the opportunity to create chats with a high level of data encryption.

Durov responded by saying that the weakening of encryption will undermine Russian national security, as “foreign intelligence agencies will inevitably get access to the entire correspondence of Russian citizens.” He added that the risk of terrorist attacks will still exist, citing as an example last year’s Paris attacks, in which terrorists used disposable phones and SMS.