ISIS takes a stronghold in Nigeria as Boko Haram pledges allegiance to the them

ISIS has taken a terrifying stranglehold on Nigeria after militants Boko Haram pledged allegiance to the terror group.

An audio recording believed to be from Boko Haram's leader Abubakar Shekau said the jihadists, who have been waging a six-year military campaign in northern Nigeria, were merging with ISIS.

A translation of the Arabic broadcast said: 'We announce our allegiance to the Caliph... and will hear and obey in times of difficulty and prosperity.'

The recording identified 'the Caliph' as Abu Bakr al-Baghdadi, the leader of ISIS and self-proclaimed caliph of the Muslim world.

The message means that ISIS now has a foothold in Nigeria, as well as controlling swathes of Iraq and Syria. 

Baghdadi has already accepted pledges of allegiance from other jihadist groups in the Middle East, Afghanistan, Pakistan and north Africa as he seeks to expand their reign of terror.

This month Boko Haram released a highly-edited video appearing to show it beheading two men in a similar fashion to the sickening footage released by ISIS.

Rita Katz, from terrorism monitor 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.' 

Chilling: The broadcast pledged allegiance to Abu Bakr al-Baghdadi, the leader of ISIS

Earlier today, four bomb blasts killed at least 50 people in the north eastern 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. 

A tricycle rider detonated a bomb when they were prevented from entering a fish market in the west of Maiduguri.

A second blast hit another market shortly afterwards before a car bomb exploded by a bus station near a government office, it was reported.

'We've received 50 dead bodies from the blast scenes and 36 injured people,' Salisu Kwaya Bura, Chief Medical Officer of Borno Specialists Hospital said.

The number of wounded was well above 36 as some of the injured were taken to two other hospitals, a hospital source said. 

Maiduguri is the birthplace of Boko Haram, which has long coveted the city as a capital for the state it wants to create. The militants tried to seize Maiduguri at the end of January and again in early February.

Boko Haram overran a territory the size of Belgium last year, which Nigeria's ill-equipped army has struggled to take back.

The group gained worldwide notoriety in April when its members kidnapped more than 200 schoolgirls.