Pavel Durov, the founder and CEO of the secure messenger service Telegram, Tweeted on October 20 that the service had been blocked in Iran after the company refused to provide the Iranian Ministry of Information and Communications Technology with spying and censorship tools. He added that after being partially disabled for about a week, the service was entirely blocked for two hours, but has since resumed full operation.
Source: Twitter.com/Durov, October 20, 2015.