Apple blocked Telegram after it was alerted “illegal content, specifically child pornography” was shared on the messaging app, although the service was since restored to the App Store.

News of both Telegram and a new app from the company called Telegram X being blocked came to light last week, but it had been unclear why.

At the time, Telegram founder Pavel Durov said Apple had informed the company “that inappropriate content was made available to our users. Once we have protections in place we expect the apps to be back on the App Store.”

In an email from Phil Schiller, Apple’s SVP of worldwide marketing, to a 9to5Mac reader, the executive explained the company blocked Telegram after “verifying the existence” of illegal content. In addition to removing the app, Apple “alerted the developer, and notified the proper authorities”, the news site quoted Schiller as saying.

The email said Apple worked with Telegram to remove the offending material and ban the users “who posted this horrible content”.

“We will never allow illegal content to be distributed by apps in the App Store…We have zero tolerance for any activity that puts children at risk – child pornography is at the top of the list of what must never occur,” Schiller added.

Telegram landed in trouble before over the content shared on its app, which offers end-to-end encryption and is touted as being very secure.

In 2017, the Indonesian government threatened to ban the app for unlawful content, particularly radical and terrorist propaganda.