France will support a bid by the African Union to win the backing of the U.N. Security Council for its five-nation force fighting Islamist militant group Boko Haram, French Foreign Minister Laurent Fabius said on Sunday.

Fabius spoke on a tour of Chad, Cameroon and Niger, countries that have launched operations against the militants who have killed thousands in a six-year war for an Islamic state in northern Nigeria.

"France's support for the integrated African reaction force is total. France will support a request of the African Union and other concerned countries for a resolution to be voted by the Security Council," Fabius said in the capital of Niger.

The African Union authorized the force combining Nigeria, Chad, Cameroon, Niger and Benin last month at a summit in Ethiopia. A Security Council resolution could give it a U.N. mandate, say senior African officials.

The force was set up in part because of a perception that Nigeria was failing to defeat the militants, who have launched a string of cross border attacks in the Lake Chad area in recent weeks, as well as killing hundreds in Nigeria.

"It is indispensable that Nigeria engages fully in the struggle against Boko Haram. Clearly, the last few actions of the Nigerian government are encouraging," Fabius told a news conference.

Nigerian forces backed by air strikes seized the northeastern border town of Baga from Boko Haram on Saturday, the military said.

Baga is at Nigeria's border with Chad, Niger and Cameroon and was the headquarters of a multinational force comprising troops from all four countries. Its recapture was an important victory, one of several in the past two weeks.

Niger will analyse parts of a missile that fell on the border town of Abadam on Tuesday killing 37 people to determine which country is responsible, said Foreign Minister Bazoum Mohamed, adding that France would help in the task. Abadam lies on the border with Nigeria.