A message allegedly from the head of Nigeria’s Boko Haram terror group Saturday pledged his group’s allegiance to Islamic State.

The pledge to IS came in an Arabic audio message with English subtitles alleged to have come from Boko Haram leader Abubakar Shekau and posted Saturday on Twitter, according to the SITE Intelligence monitoring service.

"We announce our allegiance to the Caliph of the Muslims ... and will hear and obey in times of difficulty and prosperity, in hardship and 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," said the message. IS leader Abu Bakr al-Baghdadi has declared himself the caliph.

The message was posted on Twitter, hours after Boko Haram was blamed for four suicide bomb attacks in northeastern Nigeria that killed at least 54 people and wounded more than 140 people.

The pledge comes as the Nigerian militants reportedly are massing in a northeastern town for a showdown with a multinational force that has dislodged them from a score of towns in recent weeks.

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Boko Haram has increased suicide bombings and village attacks in recent weeks as forces from Nigeria and Chad have driven the insurgents from a score of towns along Nigeria's border with Cameroon.

The insurgents also have attacked villages in Cameroon and Niger in response to Nigeria's neighbors forming a multinational force to confront the spreading Islamic uprising.

Chad's President Idris Deby this week said his forces know the whereabouts of Shekau and warned him to surrender or face death.

Boko Haram fighters are massing at their headquarters in the northeastern town of Gwoza, in apparent preparation for a showdown with multinational forces, according to witnesses who escaped from the town.

An intelligence officer said they were aware of the movement but that the military is acting cautiously as many civilians still are trapped in the town and Boko Haram is laying land mines around it.

Though there was no way to independently verify the message, it comes weeks after Boko Haram's new Twitter account broadcast that the group's Shura council was considering whether to swear formal allegiance to ISIS.

The Twitter account, increasingly slick and more frequent video messages from Boko Haram, and a new media arm all are considered signs that the group is being helped by ISIS propagandists.

Boko Haram in August followed the lead of IS in declaring an Islamic caliphate in northeast Nigeria that grew to cover an area the size of Belgium. The Islamic State had declared a caliphate in vast swaths of territory that it controls in Iraq and Syria.

The Nigerian group also began publishing videos of beheadings. The latest one, published March 2, borrowed certain elements from IS productions, such as the sound of a beating heart and heavy breathing immediately before the execution, according to SITE.

In earlier video messages last year, Shekau sent greetings and praise to both al-Baghdadi and leaders of Al Qaeda. But Boko Haram has never been an affiliate of Al Qaeda, some analysts surmise because Al Qaeda considers the Nigerians' indiscriminate slaughter of Muslim civilians as un-Islamic.

The Associated Press contributed to this report.