The number of dead has risen to at least 76 people in the accidental Nigerian air force strike on a camp for displaced people, according to the International Red Cross and Red Crescent Movement (ICRC).

ICRC said on Wednesday that six Nigeria Red Cross members were among the dead and 13 more were wounded in Tuesday's incident in Rann, in the far north of Borno state.

"In addition to aid staff, it is estimated that 70 people have been killed and more than a 100 wounded," ICRC said in a statement.

Aid group Medecins Sans Frontieres (MSF) has said 52 were killed and 120 were wounded in the incident.

 

The air force has said an unknown number of civilians were killed and wounded in the mistaken attack, which was aimed at the Boko Haram group.

Lai Mohammed, Nigeria's information minister, said "the accidental bombing is not a true reflection of the level of professionalism" he had witnessed in the air force.

Lucky Irabor, who is the theatre commander for anti-Boko Haram operations in northeast Nigeria, said the air force would not deliberately target civilians, but there will be an investigation.

Al Jazeera's Ahmed Idris, reporting from Nigeria's capital, Abuja, said: "Senior military officials say an investigation will be launched to find out exactly what happened, if there was any mistake on the part of the pilot or those conducting the operation."

WATCH: Has Boko Haram been defeated?

The air strike followed a military offensive against Boko Haram in the last few weeks.

Borno state has been the centre of Boko Haram's seven-year-long attempt to create a caliphate in the northeast.

At least 20,000 people have been killed in the Boko Haram conflict since it began in 2009 and more than 2.6 million others made homeless.

Nigeria maintains the armed rebellion is in its final stages.

Last month, the government said it had flushed out Boko Haram fighters from their stronghold in the Sambisa Forest area of Borno state, of which Maiduguri is the capital.

Yet there has been no let-up in attacks both on troops and civilians.

Boko Haram: Behind the rise of Nigeria armed group (47:40)

Source: Al Jazeera and news agencies