Islamic State (also known as Daesh) has accepted a pledge of allegiance from Nigerian militants Boko Haram who killed 10,000 people in the country last year.
The audio message entitled 'kill and be killed' and released through the militants' vast social media channels was allegedly read by an ISIS spokesperson.
As well as welcoming Boko Haram's loyalty, the speech also threatens further violence against Christian and Jewish communities according to News Week.
Speaking for his leader Abu Bakr al-Baghdadi, the man in the recording says: 'We announce to you to the good news of the expansion of the caliphate to West Africa.
'Our caliph has accepted the pledge of loyalty of our brothers of Boko Haram so we congratulate Muslims and our jihadi brothers in West Africa.'
He urged Muslims who could not join the fight in Syria to enter the conflict in Africa instead.
Nigerian President has claimed Boko Haram insurgents have already traveled to the Middle East to train with ISIS militants, according to Voice of America.
In an interview with VOAm he said: 'So we know the links are there. But even now, we may not know the degree of linkages as to how much funds are coming in from them, the kind of volume of weapons coming in from them, the nationalities coming from them.
'But the training, because some of the Boko Haram members go to have their training in the ISIS camp and come back.'
He refused to name the countries where the fighters were trained but said he has long suspected Boko Haram of already having links with other extremist groups globally.
His country has allegedly brought in hundreds of mercenaries from South Africa to aid Nigeria in its fight against Boko Haram, according to regional and military sources.
The foreign 'soldiers of fortune' were allegedly pictured on Twitter riding armoured vehicles through Maiduguri - the regional capital of Nigeria's north-east which has been besieged by terrorism.
A Reuters reporter with knowledge of the city was able to verify the location of the photo as Bama road, leading south-east out of the city.
On Wednesday, President Goodluck Jonathan said two companies were providing 'trainers and technicians' to help Nigerian forces.
The Nigerian militants first offered their allegiance to ISIS - who command territory in Syria and Iraq - over the weekend in their own audio message.
It said: 'We announce our allegiance to the Caliph ... and will hear and obey in times of difficulty and prosperity, in hardship and ease.'
The insurgents have killed thousands in bomb attacks and violent sieges on villages in the remote north-east, and are now feared to be spilling over into neighbouring Cameroon and Chad.
Members of the UN Security Council have called on the international community to supply money, equipment, troops and intelligence to the five-nation African coalition fighting them.
A draft resolution between the countries authorises the use of force against Boko Haram and Chad believes it will be approved as early as next week.
Boko Haram killed an estimated 10,000 people last year and took responsibility for last April's abduction of more than 275 schoolgirls.
The resolution demands the immediate release of anyone abducted by Boko Haram which it calls 'one of the most serious threats to international peace and security'.
The United States, Britain, France and the European Union are backing the formation of a multinational force of 8,750 troops led by Nigeria and Chad with contingents from Cameroon, Niger and Benin.
The militants have been waging a six-year insurgency to impose strict Shariah law in Nigeria and earlier this year it launched attacks across the border on Cameroon - before striking Niger and Chad.