Story highlights More than 270 girls were abducted from a school in Chibok in 2014

Some escaped immediately, one was found earlier this year

(CNN) Conflicting information is emerging about what Boko Haram received in exchange for releasing 21 Chibok schoolgirls in Nigeria this week after holding them for two years.

"A number of Boko Haram commanders" were freed as part of Thursday's release of the girls, a source close to the negotiations between the Islamist militant group and the Nigerian government said on condition of anonymity.

This contrasts with what the Nigerian government has said, which is that the girls' release was not a prisoner exchange.

Some of the released Chibok girls in Banki, Nigeria, near the Cameroon border.

"This was not a swap," Nigerian Information Minister Alhaji Lai Mohammed said Thursday. "It is a release, the product of painstaking negotiations and trust on both sides."

A separate source, one with direct knowledge about the girls' release, told CNN Thursday that no captive Boko Haram fighters were released in exchange for the girls.