Boko Haram leader Abubakar Shekau speaks at an unknown location in this still taken from an undated video released by the outfit.
Boko Haram leader Abu bakr ShekauYouTube screenshot

Radical Nigerian militant group Boko Haram has reportedly pledged a formal allegiance to the Islamic State (Isis) terrorists in Syria and Iraq, swearing to support the group 'in times of difficulty and prosperity'.

Boko Haram leader Abu Bakr Shekau reportedly released a message in which he swore allegiance to the Islamic State top boss, Abu Bakr al Baghdadi. The message was released on Twitter by Boko Haram late on Saturday, according to SITE Intel Group.

"We announce our allegiance to the Caliph of the Muslims... and will hear and obey in times of difficulty and prosperity, in hardship and ease, and to endure being discriminated against, and not to dispute about rule with those in power, except in case of evident infidelity regarding that which there is a proof from Allah," Shekau said in an English transcript of the audio obtained by Reuters.

Shekau reportedly also called on all Muslims around the world to join forces with Isis.

Rita Katz, the head of SITE Intel Group in a series of tweets noted that the development was proof that Isis is increasingly becoming popular with several such jihadist groups. Katz further noted that the gesture by Boko Haram reflects the fact that the Nigerian Islamist group is now moving up from being a  local jihadi group to being an important ally of Isis.

Reacting to this, the Nigerian government called on the international community for more support. "(The audio) confirms what we always thought. It's sad, it's bad," said Nigerian government spokesman Mike Omeri. "It's why we were appealing to the international community ... Hopefully the world will wake up to the disaster unfolding here," he told Reuters.