One hundred and twenty-one school girls abducted by Islamist group Boko Haram have reportedly been freed, but eight girls are still missing.
The Nigerian schoolgirls kidnapped by Boko Haram were taken to a stronghold of the Islamist group, parents say, as the military confirmed 129 students had been abducted.
Defence spokesman Chris Olukolade, who had earlier given the figure of those kidnapped in northeastern Borno state late on Monday, later said all but eight had been released, but that was disputed by sources in the region and could not be independently confirmed.
"The principal of the school confirmed that only eight of the girls are still missing," he said in a statement on Wednesday.
He separately told AFP that most of the students escaped immediately after they were taken by the Islamists, a claim that was not consistent with multiple witness and official accounts.
A senior security source in the region told AFP late Wednesday that more than 100 girls remained in captivity.
Borno's Governor Kashim Shettima had earlier told journalists that only 14 of the hostages had escaped so far and offered 50 million naira ($US300,000) to anyone with information that leads to the others being rescued.
The mass abduction in the Chibok area of Borno state came just hours after a bomb ripped through a packed bus station on the outskirts of Abuja, killing 75 people, the deadliest attack ever in the capital.
The bombing was also blamed on Boko Haram, a group whose five-year extremist uprising has shaken Africa's most populous country and top economy.
The state governor voiced outrage at Boko Haram, a group which says it wants to create a strict Islamic state in northern Nigeria.
"In Islam, women and children are spared during war," Shettima said.
Three of the girls who escaped and returned to Borno's Chibok area briefed locals about the attack, said Lawal Zanna, whose daughter was among those abducted.
"The girls told us they were taken to the Konduga district part of Sambisa forest by their captors," said Zanna, referring to an area where Boko Haram is known to have well-fortified camps.
The girls said they ran after getting permission from the gunmen to use the bathroom and were helped back to Chibok by nomadic herdsmen from the Fulani ethnic group.
President Goodluck Jonathan has summoned his top security chiefs to a meeting on Thursday to discuss "the security situation in the country" in the wake of the Abuja bombing and the kidnapping, his office said.
United Nations Secretary General Ban Ki-moon on Wednesday condemned the abduction, calling the targeting of schools and school children "a grave violation of international humanitarian law".
"Schools are, and must remain, safe places where children can learn and grow in peace," he said.
The gunmen stormed the Government Girls Secondary School after sundown, torching several buildings before opening fire on security forces guarding the school.
Boko Haram, whose name means "Western education is forbidden", has repeatedly attacked schools and universities in an insurgency that has killed thousands of people since 2009.
Witnesses said the gunmen killed a police officer and soldier in the shootout and ultimately forced their way into the school.
They then forced the girls outside and loaded them onto trucks and drove off into the bush of the remote region.