Twenty-one of the more than 200 Nigerian girls kidnapped from a school in Chibok by Boko Haram fighters in 2014 have been released, according to Nigeria's presidency.
The release followed negotiations between Nigeria's government and Boko Haram brokered by Red Cross and Swiss government officials, a spokesman for the country's president said on Thursday.
"It is confirmed that 21 of the missing Chibok girls have been released and are in the custody of the Department of State Services," presidential spokesman Garba Shehu said in a statement.
"The release of the girls ... is an outcome of negotiations between the administration and the Boko Haram brokered by the International Red Cross and the Swiss government," Shehu said.
"The negotiations will continue."
Lai Mohammed, Nigeria's information minister, said the released girls would arrive in Abuja later on Thursday.
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The girls were exchanged for four Boko Haram prisoners in Banki in northeast Nigeria, the AFP news agency said quoting a local source.
Later the information minister denied that any Boko Haram prisoners were for the release of the girls.
"For some time now there has been some negotiations between the Nigerian government and Boko Haram," said Al Jazeera's Ahmed Idris, reporting from the Nigerian city of Kano.
"Remember a few months ago, the leader of the Boko Haram faction that seems to be holding the girls said that they can only release these girls if the Nigerian government releases some of its commanders being held in prison across Nigeria."
The identity of the girls has yet to be confirmed, said Aisha Yesufu, a Bring Back Our Girls campaigner.
"We cannot confirm anything yet," Yesufu said.
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Boko Haram seized 276 pupils from the Government Girls Secondary School in Chibok on the night of April 14, 2014. Fifty-seven managed to escape in the immediate aftermath of the abduction.
The kidnapping has become a hot political issue in Nigeria, with the government and military criticised for their handling of the incident and their failure to rescue any of the girls.
About 2,000 girls and boys have been abducted by Boko Haram since 2014, with many used as sex slaves, fighters and even suicide bombers, according to Amnesty International, the London-based human rights organisation.
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Nigeria freed more than 500 women and children from the Sambisa forest, considered a bastion of armed group Boko Haram, in April this year.
Two abducted Chibok girls, Amina Ali Darsha and Serah Luka were rescued in May from the same forest in Borno state.
In recent months, Boko Haram has increasingly used suicide and bomb attacks as the Nigerian military pushes the group out of territories they once controlled.
But President Muhammadu Buhari has declared Boko Haram "technically" defeated, and said success in the campaign would be measured on the return of the Chibok girls and other abductees.
Source: Al Jazeera News And News Agencies