The army eventually admitted ordering the strike near the town of Rukubi, in a central region known for ethnic and religious violence, that hit a group of herders on January 24.

But in a response to Human Rights Watch (HRW) dated May 17, the army said it had targeted "alleged terrorists" based on "credible information", without admitting any fault.

"The military's unacceptable delay in owning up to the killing and injuring dozens of civilians only compounds the tragedy of this shocking attack," HRW's Africa researcher Anietie Ewang said in a statement.

"The Nigerian military should provide full accountability for their actions as well as financial compensation and livelihood assistance commensurate with the needs of the victims and their families," she said.

Army officials declined to comment immediately when contacted by AFP on Tuesday.

Security forces regularly carry out airstrikes in northwest and central Nigeria against Islamist insurgents as well as criminal gangs, at times accidentally hitting civilians.