Nigeria’s militant Islamist group Boko Haram has pledged allegiance to Islamic State, which rules a self-declared caliphate in parts of Iraq and Syria, according to a video posted online Saturday.

“We announce our allegiance to the Caliph … and will hear and obey in times of difficulty and prosperity,” read an English-language translation of the video broadcast in Arabic that purported to be from the Nigerian militant group.

The pledge of allegiance was attributed to Boko Haram leader Abubakar Shekau.

The video script identified the Caliph as Ibrahim ibn Awad ibn Ibrahim al-Awad al-Qurashi, who is better known as Abu Bakr al-Baghdadi, the leader of Islamic State and self-proclaimed caliph of the Muslim world.

Baghdadi has already accepted pledges of allegiance from other jihadist groups in the Middle East, Afghanistan, Pakistan and north Africa.

Boko Haram has been waging a six-year military campaign to carve out an Islamic state in northern Nigeria. On Saturday, four bomb blasts killed at least 55 people in the northeastern Nigerian city of Maiduguri in the worst attacks there since Boko Haram militants tried to seize the town in two major assaults earlier this year.