The mother of a kidnapped Chibok schoolgirl is demanding that Nigeria's president free detained Boko Haram militants in exchange for the more than 200 girls held captive, as the Islamic extremists have offered.

At least 218 Chibok girls are missing after being abducted from a remote school in April 2014.

A new Boko Haram video shows dozens of the abducted girls with one saying that "some" have died in military air strikes. Nigeria's defense ministry is disputing that, saying it is rare for innocent civilians to be killed in the bombings.

Esther Yakubu, the mother of a kidnapped girl who begs to be freed in the new video, says the government should just release the militants.

But officials say they don't know who to negotiate with.