Nigeria's defence chief has defended operations against insurgents and criminal gangs that have caused civilian casualties, saying the military is doing what it can to prevent loss of life.

Nigeria's military has increasingly used airstrikes against the growing threat of militias in the north and central regions. It has admitted to mistakenly targeting civilians while pursuing armed gangs in the northwest, where there is widespread insecurity, and has promised to investigate such cases.

Defence Chief of Staff General Christopher Musa also called for a review of international laws, arguing that they restrict state forces while leaving non-state actors "who kill at will" unchecked.

In rare comments to reporters in the capital Abuja on Wednesday, Musa said the military frequently halts operations to prevent civilian harm, even at the cost of compromising tactical advantages.

"We are made to look as if we are committing the worst atrocities ever, but I can assure you that we are doing the best we can. We respect human rights and value civilian lives," he said.

"We often abort operations to avoid civilian casualties ... this has, in part, prolonged the conflict."

The remarks come after growing scrutiny of Nigeria's counterinsurgency operations and accusations by rights groups that the military has used excessive force.

But there are frustrations within Nigeria's armed forces, where many believe they are being judged against higher standards than comparable forces in more developed countries.

They also say too little account is taken of the difficulties of fighting informal armed Islamist insurgents or criminal gangs who operate entirely among civilians.

The general cited ongoing training in human rights and international humanitarian law for military personnel, both locally and abroad, as evidence of progress.