All of the schools in the area had been closed because of a recent spate of terrorist attacks in which students were the apparent targets.
The incident triggered global outrage and raised calls for close security cooperation to fight terror cells in the region.
While international efforts were underway, about 50 of the girls have so far managed to escape from their abductors.
Some members of the Islamist militant group have been arrested and international efforts were under way to rescue the schoolgirls.
Boko Haram meaning "western education is a sin", since its formation in 2002 has killed about 10,000 people. The group has killed about 1,500 Nigerians since the beginning of this year.
