The Nigerian government has given an insight into the negotiations that led to the release of 21 Chibok school girls.
A confirmation the girls had been freed came Thursday morning.
The girls over 200 were abducted by the extremist sect Boko Haram on April 14, 2014, from a secondary school in Chibok.
Some 50 of the girls managed to escape and about 218 of them are still missing.
Previous efforts by two Nigerian administrations to free the girls were not successful.
The latest success came after the intervention of the Red Cross and the Swiss government.
“The release of the girls, in a limited number is the outcome of negotiations between the administration and the Boko Haram brokered by the International Red Cross and the Swiss government,” a statement issued by presidential spokesperson, Garba Shehu, said.
He said the talks will continue.
Separately, officials briefed about the deal revealed that the girls were swapped for four Boko Haram insurgents. Names of the militants were not released.
Boko Haram demanded the release of its members held by the government, as condition for freeing the girls.
The officials stated that the exchange took place Wednesday night when Nigerian military officials, alongside personnel of United Nations, Red Cross and National Emergency Management Agency, conveyed four Boko Haram militants by a chopper to Banki, a border town in Bama local government area of Borno State.
There, 21 released girls were picked up. The girls were brought into Maiduguri Air Force base at about 8.30a.m.
A source said most of the girls had babies.
They were immediately flown to Abuja at 9a.m.
Many residents of Maiduguri were woken by the sounds of aircraft hovering in the air Thursday morning.