The Nigerian government has claimed that a splinter of the Boko Haram terror group is holding 83 girls kidnapped by the Islamists and is willing to negotiate their release. The captives are part of a group of 219 schoolgirls abducted from Chibok, a village in the restive Borno state, in April 2014.

"The Mamman Nur faction of the Boko Haram has indicated its willingness to negotiate the release of more Chibok girls in their custody. The group claims that it has 83 more girls to release on negotiation," presidential spokesperson Garba Shehu told news agency AFP.

The claim came shortly after the government announced that 21 Chibok girls had been released on 13 October by Boko Haram in negotiations brokered by Switzerland and the Red Cross.

Reports alleged that the government had freed some militants in exchange for the girls, something authorities have denied.

One Chibok girl was rescued in the Sambisa forest earlier this year. Following recent developments, it is believed at least 197 are still missing.

Although the Chibok abduction was not the first mass-kidnapping carried out by Boko Haram, it was the only one that attracted international outrage.

It led to the creation of the global movement Bring Back Our Girls, which shone a spotlight on the deadly insurgency of Boko Haram that had previously been under-reported.

Mamman Nur and Boko Haram's three factions

Mamman Nur is believed to be part of a group of people who defected from Boko Haram to form the Vanguard for the Protection of Muslims in Black Lands (Ansaru), in 2012. Nur has become an influential figure within the breakaway group.

Ansaru logo Wikimedia Commons

Who are the Ansaru terrorists?

Ansaru operates in northern and central Nigeria and, unlike Boko Haram, does not attack Muslim civilians or force women and children to carry out suicide bombing missions.

Its leader, Khalid al-Barnawi, who is now in DSS (Department of State Services) custody, said in the first statement the group released after its formation that Boko Haram actions were "inhumane" to Muslims.

Ansaru has been linked to the al-Qaeda in the Islamic Maghreb (Aqim). It is also believed the group has increasingly sought cooperation with IS.

Although Ansaru is a faction of Boko Haram, it is believed the two groups reintegrated in the Nigerian-Cameroon border region, where they exchange resources and militants.

More on the Ansaru group here.

Some analysts believe that the future development of Boko Haram could depend on Nur, given his connection to international terror groups.

Earlier this year, Boko Haram split into two factions after its leader Abubakar Shekau was replaced with Abu Musab Al-Barnawi, former Boko Haram spokesperson.

The new appointment was made by Boko Haram's ally, the Islamic State (Isis/Daesh) terror group.

Shekau, however, denied he had been replaced and claimed al-Barnawi was staging a coup against him.

Before the government claimed that the Mamman Nur faction said it was in possession of the girls, some analysts believed the Chibok girls were held by Shehaku.

Earlier in October, the contested leader released a video message urging the government to free detained militants in exchange for the Chibok girls.

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Who are Nigeria's Boko Haram?

Boko Haram, which has renamed itself Iswap, fights against Western influence in Nigeria and aims to impose its version of Sharia law throughout occupied territories.

The group launches attacks in Nigeria and neighbouring countries in a bid to take control of more territory. Three Nigerian states – Adamawa, Borno and Yobe − have been under a state of emergency since May 2013.

Boko Haram has killed more than 20,000 people since 2009 and was deemed the world's deadliest terror group, surpassing Islamic State in November 2015. Nigeria has also become the world's third-most terrorised country as a result of the group's violent insurgency.

Chibok girls
Some of the 21 Chibok school girls released are seen during a meeting with Nigeria's Vice President Yemi Osinbajo in Abuja, Nigeria, 13 October, 2016 Sunday Aghaeze/Special Assistant to Nigerian President Muhammadu Buhari/Handout via REUTERS