The Islamic State group has welcomed a pledge of allegiance made to it by Boko Haram and vowed to press with its expansion, according to an audiotape Thursday purportedly from its spokesman, the AFP is reporting.

“We announce to you to the good news of the expansion of the caliphate to West Africa because the caliph… has accepted the allegiance of our brothers of the Sunni group for preaching and the jihad”, IS spokesman, Mohammed al-Adnani said in the message, using the Arabic name for Nigeria’s Boko Haram extremist group.

In the tape of some 30 minutes, the IS spokesman called on Muslims to join fellow extremists in West Africa and downplayed “victories” by the US-led coalition and Iraqi forces against his group.

It would be recalled that following heavy bombardment of Boko Haram terrorist group in Northeastern Nigeria by Nigerian Armed Forces and its counterparts from Cameroon, Niger and Chad, an audiotape purportedly released by the group’s leader, Abubakar Shekau on Saturday, said “we announce our allegiance to the Caliph of the Muslims, Ibrahim ibn Awad ibn Ibrahim al-Husseini al-Qurashi”, referring to IS leader Abu Bakr al-Baghdadi.

Security analysts have said that pledge may only have propaganda value in the short term but could lead to closer links in the future.