Isil extremists are using Instagram to promote jihad and incite support for terror attacks on the West, an investigation by The Telegraph has found.

They are circumventing the platform’s security checks to post images and text celebrating the killings of “kafir” (unbelievers) accompanied by images of dead soldiers and beheadings as well as threatening terrorist atrocities on the scale of the Sri Lankan suicide bombings that claimed 253 lives.

Some posts brazenly use Isil’s logo or images of Abu Bakr al-Baghdadi, the self-proclaimed leader of the Islamic State of Iraq and the Levant, as their profile pictures and urge followers to join jihad.

The investigation exposes serious flaws in the ability of the social media giants to police their sites and prevent extremists exploiting them to promote their causes.

It also found live-streamed footage of white supremacist Brenton Tarrant’s attack on mosques in New Zealand was still up on Facebook’s site and had been for two months since the atrocity in which 51 people including children were fatally shot.

After being alerted to the posts by The Sunday Telegraph, Instagram and Facebook removed the accounts and video, admitting they violated their guidelines and insisting they would not tolerate terrorism on their sites.