Ninety-eight of the 276 students kidnapped by the militants from Government Girls Secondary School, Chibok, in the north-eastern Borno State, are still in captivity.

The incident sparked local and international outrage with leaders and activists exerting pressure on the Nigerian government to act.

So far, 178 of the girls have escaped but many of returned home traumatised, some with children sired by Boko Haram militants, local media report.

“Our hearts remain broken at the failure to close this shameful chapter in our country’s history as promised by President Muhammadu Buhari in his address to the nation in 2015 and various times subsequently," BBOG said in a statement.

“Provide closure for parents on the fate of their daughters who they have reason to believe are dead," the statement added.

Asabe Kwambura, who was the head of Chibok school at the time of the abduction, told the Daily Trust newspaper that she was yet to recover from the shock.

The chairman of the Chibok Parents Association, Yakubu Nkenki, appealed to the government to seek the release of the remaining girls.

In a statement, Amnesty International Nigeria said parents of the Chibok girls are "living in anguish" stressing that the missing girls should be returned home to their families and all those responsible face justice.