Eight girls remain missing.
Maj. Gen. Chris Olukolade reported that one of the alleged kidnappers had been captured and that a search and rescue mission was underway to "ensure the safety of the remaining students."
There was no further information regarding the circumstances of the girls' release and their conditions were not known.
Initial reports indicated that 200 school girls had been kidnapped.
Earlier Wednesday, United Nations Secretary-General Ban Ki-moon issued a statement condemning "the shocking mass abduction" and expressed alarm "about the increasing frequency and brutality of attacks against educational institutions in the north of the country."
"The targeting of schools and school children is a grave violation of international humanitarian law. Schools are, and must remain, safe places where children can learn and grow in peace."