The extremist Islamic group Boko Haram has pledged allegiance to the leader of the Islamic State, ISIS, Abubakr Al-Qurashi.

Abubakar Shekau,  leader of the Boko Haram group which is responsible for acts of terror and insurgency in the North east and in neighbouring country such as Cameroon, Chad, and Niger, made the pledge in an audio recording released on Saturday via the Internet.

The announcement was released in audio format, a marked departure from former instances in which the group released video clips to communicate with the public.

The audio message announced the group’s allegiance to the cause of ISIS, with a vow to obey ISIS leadership in times of prosperity and difficulty.

Shekau stated that the decision to form an alliance with ISIS was in accordance to divine provisions in the Quran and in obedience to the instruction of founder of Islam, Prophet Mohammed.

“We announce our allegiance to the caliph of the Muslims, Ibrahim ibn Awad Ibrahim al-Husseini al Qurashi, and will hear and obey in times of difficulty and prosperity, in hardship and in 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,” the group announced in the audio message.

The group also urged Muslims across the world to pledge allegiance to the caliph and support him, stating that it is their duty to submit to “an Imam that looks after them according to Allah’s rule and fights the enemies of Islam and those who fights the Rule of Allah” and that being united “under one Jamaa’ah” is prerequisite for success in their undertaking.

The group also encouraged unity amongst all Muslims, stating that it would “enrage the enemy of Allah, by Allah, our gathering under one banner, under one Imam, is more heavy to the enemy”.

Boko Haram has pursued an agenda of establishing an Islamic caliphate in Northern Nigeria while ISIS, which operates across the Middle East, has occupied large territories in Iraq and Syria.

Both groups have engaged in the devastation of cities and town, murdering thousands in their respective regions.

Boko Haram had recently adopted the ISIS media strategy, including the release of well-produced videos, which are sub-titled in French and Arabic.

The group also recently opened and operated a Twitter account like ISIS did, until it was shut down by the tech company.