A Nigerian journalist with links to the Islamist group Boko Haram has claimed only 15 out of the 112 missing Chibok girls are still alive.
Ahmad Salkida said he had negotiated for the release of the girls on the behalf of the government.
Several opportunities to have them released were missed, Mr Salikda said.
A spokesperson for the government told the BBC that it was still in discussions with Boko Haram to secure the release of the 112 girls.
He said that there was no reason to believe some of the girls may be dead.
Mr Salkida said the administration of former President Goodluck Jonathan had asked him to negotiate for the release of the Chibok schoolgirls two weeks after they were abducted.
He said he had arranged for a prisoner swap on five occasions, but delays from the then government led to a breakdown in negotiations.
Mr Salkida would not reveal the names of the remaining girls, stating that this was the responsibility of the Nigerian government.
The 276 schoolgirls were abducted by Boko Haram exactly four years ago, on 14 April 2014.
