A multinational force being set up to combat Nigeria's Boko Haram Islamist insurgency in the Lake Chad region will be operational in the coming weeks, Niger's President Mahamadou Issoufou said on Tuesday.

Approved in March by the African Union, the 8,700-strong force drawn from the Lake Chad countries of Niger, Nigeria, Chad, Cameroon as well as Benin, will be financed partly by the international community.

"We have discussed the situation on our southern side with Boko Haram rampaging in the Lake Chad zone," Issoufou told reporters outside the Elysee Palace in Paris after a meeting with French President Francois Hollande.

"We think that in the coming weeks, with the new administration settling into place in Nigeria, we are going to be able to launch the mixed multinational force, to which all of the countries of the Lake Chad basin contribute," he added.

As he spoke, sources in Nigeria's northeastern city of Maiduguri reported that a bomb blast hit a busy market there on Tuesday, killing as many as 50 people.

An Elysee statement said Hollande told Issoufou that France would "continue its logistical support and intelligence to the countries neighbouring Lake Chad" to combat the group thought to have killed thousands of people in its quest to create a caliphate in Nigeria's remote north-east.

The new president of Nigeria, Muhammadu Buhari, the first to take power in a democratic handover in the history of the country, promised to eradicate Boko Haram in an inaugural address last week.