Nigeria denies paying ransom and freeing Boko Haram leaders for Chibok girls
Security experts say it is unlikely the 21 girls released on Thursday were freed without a significant incentive
The Nigerian government has denied reports that it paid millions of dollars and released senior extremist leaders to convince Islamist militants to free 21 girls abducted more than two years ago.
The girls, who were released early on Thursday morning, were among 276 female students taken from their hostel in a government boarding school in the small town of Chibok in April 2014 by Boko Haram. They were handed over to the government at a remote location in northern Nigeria.
Boko Haram has waged a violent insurgency in the north of Africas most populous nation for seven years.
The kidnapping of the girls brought the group international infamy and led to the global campaign #BringBackOurGirls, which featured public figures including the US first lady, Michelle Obama.
Officials have confirmed that the Swiss government provided mediators during negotiations, while the International Committee of the Red Cross provided medical assistance during the transfer of the girls.
Security experts say it is unlikely the girls would have been released by the group, which has split into two major factions, without a significant incentive.