21 of the Chibok schoolgirls kidnapped by Boko Haram have been freed, BBC reported on Thursday, citing a senior Nigerian government official.
The official wanted to remain anonymous and the government has not issued a statement. Previous reports of the girls' release have turned out to be wrong.
The Islamist militant group kidnapped more than 270 students from a school in Chibok in April 2014 - an act that provoked international condemnation. It also sparked one of the biggest global social media campaigns, with tweeters using the hashtag #BringBackOurGirls.
Nigerian government later on the day confirmed the release of 21 schoolgirls.
"The release of the girls ... is the outcome of negotiations between the administration and the Boko Haram brokered by the International Red Cross and the Swiss government," a presidency statement said, adding that negotiations will continue.
The presidency gave no details on the deal, saying only that the 21 girls were very tired and would first rest in the custody of the national security agency.
There has only been one confirmed release of a student kidnapped from Chibok more than two years ago. In May, a 19-year-old woman
was found carrying by an army-backed vigilante group.
After that it was believed that 218 students
were still missing - more than 50 managed to escape on the day they were captured.
Boko Haram has also kidnapped thousands of other people during its seven-year insurgency in north-east Nigeria.