Hacktivist group Anonymous has vowed to attack terrorist websites and social media accounts in revenge for the killing of Charlie Hebdo journalists.

A Belgian offshoot of the group posted a video to the website “declaring war” against terrorist groups.

In the message, in French and addressed to “Al Qaeda, Islamic State and other terrorists” in its description, the group says that it will take down the websites and social media accounts of terrorist groups.

The group also posted a message to Pastebin, also in French and addressed to the “enemies of the freedom of expression”.

The video is narrated by a man wearing the group’s distinctive Guy Fawkes mask and with his voice obscured. It calls the operation #OpCharlieHebdo, in keeping with the group's usual naming conventions.

The video has had over 177,000 views since it was posted yesterday. Comments are turned off, but the video has received over 2,600 likes, against hardly any dislikes.