UN Secretary-General Ban Ki-moon on Saturday welcomed an African Union proposal to set up a regional five-nation force of 7,500 troops to fight Nigeria's Boko Haram Islamist militants.

"I welcome the decision of the AU and regional countries to establish an MJTF (Multinational Joint Task Force) against Boko Haram. They have committed unspeakable brutality. Those terrorists should be addressed with a regional and international cooperation," he told reporters during an African Union summit being held in the Ethiopian capital.