The leader of the Nigerian Islamist group says his fighters will obey Abu Bakr al-Baghdadi, the self-styled “caliph” whose followers have seized swathes of Iraq and Syria.
Boko Haram‘s leader, Abubakar Shekau made the oath in an Arabic audio clip posted on Twitter.
He said: “We announce our allegiance to the caliph … and will hear and obey in times of difficulty and prosperity, in hardship and ease. We call upon Muslims everywhere to pledge allegiance to the caliph.”
The unverified statement was reported by the SITE intelligence monitoring service, a Washington group which tracks statements and videos released by extremists.
The audio script identified the caliph as al-Baghdadi, the self-proclaimed leader of the Muslim world.
Nigerian government spokesman Mike Omeri said: “(The audio) is confirming what we always thought. It’s sad, it’s bad.
“It’s why we were appealing to the international community… Hopefully the world will wake up to the disaster unfolding here.”
Boko Haram has killed thousands of victims and kidnapped hundreds during its six-year campaign to carve out an Islamist state in northern Nigeria. In recent months it has increased cross-border raids into Cameroon, Chad and Niger.
On Saturday, four bomb blasts killed at least 50 people in the northeastern Nigerian city of Maiduguri.
Boko Haram militants are reportedly massing in a northeastern town for a confrontation with a multinational force that has dislodged them from a score of towns in recent weeks.
Al-Baghdadi has already accepted pledges of allegiance from other jihadist groups in the Middle East, Afghanistan, Pakistan and north Africa.
This month, Boko Haram released a video purporting to show the beheading of two men, using advanced graphics and editing techniques similar to seen in Islamic State propaganda.
Laith Alkhouri, director of the Middle East and North Africa research and jihadi threat intelligence at Flashpoint Partners, said the devlopment did not come as a surprise to experts who have been monitoring the Nigerian group.
“Boko Haram has followed a trend that only led (us) to anticipate the release of this audio, mimicking Islamic State propaganda and approach to military methods, and calling its fighters soldiers of the caliphate.
“The Islamic State, unlike al-Qaeda, did not seem to shun Shekau. It accepted his thuggish persona and lack of Islamic knowledge.”
Rita Katz, director of SITE Intelligence Group, said: “Boko Haram is now being elevated from a local jihadi group to an important arm of the Islamic State.
“With Boko Haram’s wide network in North Africa, the Islamic State’s projection of creating an Islamic caliphate is gaining headway.
“Furthermore, Islamic State’s infrastructure, resources and military capabilities will enable Boko Haram to expand its operations and control even faster in North Africa.”