Extremist group Islamic State in Iraq and Syria (ISIS) has reportedly turned to popular mobile messaging app Telegram to fuel its propaganda push.

According to the BBC, Twitter's crackdown on ISIS' accounts has led the group to seek alternatives - and Telegram appears to be a suitable outlet.

A new feature on the app allows users to broadcast their messages to any number of members via their own Telegram "channel".

ISIS currently has a channel with more than 4,500 subscribers.

The group uses it as a tool to announce its activities, coordinate attacks and even claimed responsibility for recent bombings in the Yemeni city of Aden.

And while the Berlin-based Telegram - launched in August 2013 by Russian brothers Nikolai and Pavel Durov - is similar to other apps in the market such as WhatsApp and LINE, its "high level of encryption" and secure platform appeals enormously to ISIS.

Having claimed to be the "fastest and most secure messaging system in the world, it once offered a hefty reward of US$300,000 (S$419,000) in bitcoins to the first person who cracks its encryption and intercept a daily message between the Durov brothers.

On its part, Telegram states on its website that it is open to taking down illegal public content and will block terrorist (for instance, ISIS-related) bots.