Nigeria is hosting an international summit on Saturday to discuss the violence caused by extremist group Boko Haram.

Nigerian president Muhammadu Buhari welcomed leaders from West and Central Africa — from Benin, as well as Chad, Niger and Cameroon, where the Islamist group has launched attacks..

French President Francois Hollande and high-ranking diplomats from the U.S., U.K. and European Union are also attending the talks in the Nigerian capital, Abuja. Upon his arrival, Hollande spoke of the challenges facing Nigeria and some of the progress in battling the militants.

"Nigeria has been the main battleground. And do you know when we came in, Boko Haram was holding at least 40 local governments out of the 770 local governments we have. And they have forced their flag, and they call the place a caliphate. Which kind of caliphate they didn't say, but they called it a caliphate. But now they are not holding any local governments."

Image | Boko Haram Nigeria Damasak

Caption: In November 2014, 400 women and children were abducted in the remote Nigerian border town of Damasak. The kidnapping garnered far less attention than the 276 school girls taken from Chilbok seven months earlier. This young girl managed to avoid the Damasak kidnapping. (Joe Penney/Reuters)

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The United Nations Security Council has expressed concern over the terror group's links to ISIS and is calling the summit a "crucial initiative."

In a statement issued Friday, the council called on Boko Haram to "immediately and unequivocally cease all violence and all abuses of human rights and violations of international humanitarian law."

It also demands the immediate release of the thousands of people held captive by Boko Haram, including 219 Nigerian schoolgirls abducted in April 2014.

Some 20,000 people have died and 2.1 million become refugees in Boko Haram's nearly seven-year uprising to create an Islamic state, but U.S.-backed African governments have made military advances against Islamic extremists.

Seven months after the abduction at the school in Chibok, Boko Haram stormed another school in Damasak, using it as a military base, before withdrawing in March 2015. About 300 elementary school students were among their 400 captives.

Mausi Segun, a Nigeria researcher for Human Rights Watch, recently said those children remain missing.

"We know that it is not just 219 missing schoolgirls, that Amnesty Internatioinal estimates there are more than 2,000 women and children who have been abducted by Boko Haram," said freelance journalist Anna Cunningham, reporting from Lagos.

Last year, the extremist group released a video pledging their official allegiance to ISIS.

There are concerns over reports that Boko Haram fighters are now in Libya and are training and fighting there alongswide ISIS.