The head of the African Islamist militant group Boko Haram has made light of the multi-national task force that was assembled to combat its ranks, the AFP news agency reports.

"Your alliance will not achieve anything," said the group's leader,Abubakar Shekau, mocking the regional army in a 28-minute video released on YouTube over the weekend.

He then challenged the coalition to face his forces in battle.

"Amass all your weapons and face us. We welcome you," he said.

All four countries in the Lake Chad Basin - Nigeria, the Niger, Chad and Cameroon - together with the nation of Benin in Nigeria's western border agreed on Saturday to form the regional force over concerns of Boko Haram's threat to the region.  The terrorist group has openly threatened Cameroon and Niger after gaining ground in northeast Nigeria.

Shekau mocked the size of the regional force, which is planned to be composed of roughly 8,000 personnel.

"You send 7,000 troops?" he said. "By Allah, it is small. We can seize them one-by-one." He then challenged the coalition to send in 70 million troops.

Shekau also issued a direct threat to Idriss Deby, Chad's president, apparently for its active involvement in curbing his group's activities. 

Before the formal organisation of the force, regional heavyweight Chad had already lent military support to both Nigeria and Cameroon to combat the Islamist group. Chadian forces have assisted Nigerian soldiers in gaining back territory in northeast Nigeria in the past two weeks. 

Shekau's video referenced the battle of British colonial forces and the Sokoto caliphate, as well as the leader of the Islamic State of Iraq and Syria, Abu Bakr al-Baghdadi in what could be an attempt to position Boko Haram in a global context.

"We never rose up to fight Africa. We rose up to fight the world," he said.

"We are going to fight the world on the principle that whoever doesn't obey Allah and the Prophet to either obey or die or become a slave," the Boko Haram leader added.