Mr Buhari noted that Boko Haram had exacted heavy toll in terms of lives and resources in Nigeria and some neighbouring countries.
President Muhammadu Buhari has emphasized the need for countries rocked by security challenges in the West African sub-region and those in the Sahel to team up to confront the menace.
Femi Adesina, the President's spokesman, said Buhari stated this when he received the new Special Representative of the UN Secretary-General for West Africa and the Sahel (UNOWAS), Mahamat Saleh Annadif, at the State House, Abuja, on Tuesday.
The president said: "You are our neighbour. You have vast experience on matters affecting the Sahel, having served for five years in Mali.
"I hope you will get the countries to work together to confront the issues affecting them."
While describing the problems as "enormous," Mr Buhari noted that Boko Haram had exacted heavy toll in terms of lives and resources in Nigeria and some neighbouring countries.
He added that Mali equally had a large swathe of the country occupied by militants.
He submitted: 'I hope under the auspices of UNOWAS, you will help get the problems sorted out. Most of them have to do with the instability in Libya, and it affects all of us."
The president pledged the assistance of Nigeria to the Special Representative, so that he could succeed in his assignment.
Mr Annadif, a Chadian, said he was visiting shortly after his appointment, because he recognised the crucial role of Nigeria in West Africa.
He said he was quite familiar with the problems of the Sahel region, and would depend on the help of Nigeria to succeed.