The Islamic State (ISIS) group has accepted a pledge of allegiance to the group made by the Nigerian jihadist organization Boko Haram, according to an audiotape Thursday purportedly from its spokesman.
"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," ISIS spokesman Mohammed al-Adnani said in the message, using the name in Arabic of the Nigerian group, reports AFP.
Itself a radical Sunni Muslim movement, ISIS has seized large swathes of Iraq and Syria and declared an Islamic "caliphate" there, and has also drawn expressions of allegiance from jihadists in Egypt and Libya.
On Saturday, an audiotape attributed to Boko Haram leader Abubakar Shekau said "we announce our allegiance to the Caliph of the Muslims, Ibrahim ibn Awad ibn Ibrahim al-Husseini al-Qurashi," referring to ISIS leader Abu Bakr al-Baghdadi.
Shekau has previously mentioned Baghdadi in video messages, yet stopped short of pledging formal allegiance.
But there have been increasing signs that the Nigerian terrorists, whose six-year insurgency has claimed more than 13,000 lives and left 1.5 million people homeless, have been seeking a closer tie-up.
One such sign was seen when Boko Haram terrorists followed in the path of ISIS after it burned a Jordanian pilot to death, sparking the Nigerian terrorists to burn over 90 civilians to death in Cameroon.
ISIS spokesman Adnani urged Muslims to join terrorists in West Africa and insisted that the caliphate was growing.
"Our caliphate is resisting and it is advancing in the right direction. We are fighting the Crusaders and the rafidah (Shi'ites) and day by day the Islamic State is becoming strong," he said.
He insisted that the jihadist group is "sure of its victory" regardless of the challenges it is facing.
For months, ISIS has been targeted with air strikes from a coalition led by the United States and suffered territorial setbacks in Syria and Iraq. And Iraqi government forces have closed on the city of Tikrit this week in a bid to retake it from the group.