Nigerian soldiers have freed most of the more than 100 female pupils who were abducted by armed men in the northeast state of Borno, according to the country's military.

Major General Chris Olukolade, a spokesman for the military, said on Wednesday that one of the men involved in Monday's abduction of students from the Chibok government secondary school had been captured.

"With this development, the principal of the school has confirmed that only eight of the students are still missing," Olukolade said, adding that forces were continuing to search for them.

Olukolade would not specify how many had been rescued or give details on how or where they were freed.

But the school's principal said she could not confirm the military report that more than 100 female students kidnapped were free.

Asabe Kwambura told the Associated Press that only 14 of the 129 abducted students had returned to Chibok town, with the rest still missing.

The attackers killed a soldier and police officer guarding the school before abducting the pupils, according to an official.

"When we saw these gunmen, we thought they were soldiers, they told all of us to come and walk to the gates, we followed their instructions," Godiya Isaiah, an 18-year-old who managed to flee from her abductors, told the Reuters news agency.

Ongoing instability

The abduction of the pupils, between the ages of 15 and 18, happened on the same day that a bomb blast killed at least 75 people near the capital, Abuja.

In other attacks, at least 20 people were killed in Nigeria's northeast on Wednesday, according to local government and security officials.

No one has claimed to have carried out the kidnappings or the attacks, but the armed group Boko Haram is suspected of being behind them.

The group's fighters have repeatedly attacked schools in the northeast as part of a rebellion that has killed thousands since 2009.

Boko Haram is against the education of women and its fighters are known to be abducting girls to use as cooks and sex slaves.

A spokesman for Nigerian president, Goodluck Jonathan, Reuben Aabati, said that the president had ordered the military to secure the release of all the missing girls and called a meeting of his national security council for Thursday to review the security situation in the country.

Jonathan is under pressure to contain sectarian violence in Nigeria before the country's next election, which is expected to take place in February.