More than 40 armed men and four Nigerian soldiers died in clashes near the scene where scores of abducted schoolgirls are believed to be held in the north of the country, the military has said.

"The capture of a number of terrorists believed to be the ringleaders of those operating around Alagarmo sparked a major fight on the outskirts of Bulanbuli, Borno State last night," defence spokesman Major General Chris Olukolade said in a statement on Friday.

He also added that nine soldiers were wounded.

Bulanbuli is between Alagarmo and Sambisa forest where the students, who were abducted early last week, are believed to be held.

The April 14 kidnapping of at least 230 schoolgirls came hours after the deadliest attack yet in Nigeria's capital - a bomb blast at a crowded bus station, killing at least 75 people. Boko Haram leader Abubakar Shekau claimed responsibility for that attack.

The safe release of the schoolgirls topped the agenda of a meeting Nigerian President Goodluck Jonathan held on Thursday with political and military chiefs, a governor had said. But it is not clear if the latest clash with the fighters was part of new security measures taken after that meeting.

Army assault

Residents of the town where the school is located reported hearing at least 30 explosions coming from nearby Sambisa forest where the fighters have a camp.

"For most of the night we kept hearing huge explosions from afar coming from Sambisa forest," a resident, Haladu Sule told AFP news agency. Another resident, Adamu Abdullahi, gave a similar account saying residents could not sleep "thinking the town would be attacked".

"We believe the explosions were from deep inside Sambisa forest where our girls are being held by Boko Haram but we don't know if it is a rescue operation by soldiers to free the girls," said Enoch Mark, whose daughter and two nieces were among the kidnapped girls.

Borno government said 129 students were taken from the Government Girls Secondary School in Chibok when the gunmen stormed the town at night, however, the school's principal Asabe Kwambura, who later said she was working with parents to compile a complete registry of those taken, put the figure of girls abducted at 230.

Forty-three girls escaped from their captors while 187 were still in the custody of the fighters, according to the principal and officials.

The mass abduction in Chibok was blamed on the Boko Haram armed group.

It has been described as one of the most shocking attacks in the armed group's five-year conflict which has claimed thousands of lives.