The service said it had shut down 78 channels across 12 languages this week, and improved ways for users to report illegal or objectionable activity on Telegram.
It came after Isil issued guidelines to its members on how to avoid being hacked by activists and governments via a channel on the Telegram app.
Telegram was founded as a privacy-centric messaging app two years ago by Nikolai and Pavel Durov, who founded Russian social network VK. It is functionally similar to WhatsApp in some ways, but claims much better security features, such as "secret chats" that uses end-to-end encryption and self-deleting messages.
Telegram also lets users subscribe to "channels" - public accounts that can broadcast messages to a large number of users. The official "Telegram News" channel, for example, has almost 35,000 subscribers.
In a statement on Telegram News, the service said: "We were disturbed to learn that Telegram's public channels were being used by ISIS to spread their propaganda.
"We are carefully reviewing all reports sent to us at abuse@telegram.org and are taking appropriate action to block such channels. As a result, this week alone we blocked 78 ISIS-related channels across 12 languages.
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