A Nigerian army drone targeting armed groups killed at least 85 civilians by mistake on Sunday in northwest Kaduna State, causing outrage over one of the country's deadliest military bombing accidents.

Calling the incident "disturbing", President Bola Ahmed Tinubu ordered an investigation Tuesday after the army acknowledged one of its drones mistakenly struck the village of Tudun Biri as residents celebrated a Muslim festival.

The UN human rights office said it deplored the attack, noting that it was the latest of at least four airstrikes that have resulted in significant civilian fatalities since 2017.

"While we note that the authorities have termed the civilian deaths as accidental, we call on them to take all feasible steps in future to ensure civilians and civilian infrastructure are protected," spokesman Seif Magango said in a statement.

"They must review rules of engagement and standard operating procedures to ensure that such incidents do not happen again."

Militia gangs, known locally as bandits, have long terrorised parts of northwest Nigeria, operating from bases deep in forests and raiding villages to loot and kidnap residents for ransom.

The military said troops were carrying out aerial patrols when they observed a group of people and "misinterpreted their pattern of activities to be similar to that of the bandits", before the drone strike was launched.

"We are particularly alarmed by reports that the strike was based on the 'pattern of activities' of those at the scene which was wrongly analysed and misinterpreted," said Magango.

"There are serious concerns as to whether so-called 'pattern of life' strikes sufficiently comply with international law."

After coming to office in May, Tinubu said tackling insecurity was one of his key concerns as he looks to bring more foreign investment to Africa's most populous nation.

Nigeria's armed forces often rely on airstrikes in their battle against bandit militias in the northwest and northeast of the country, where jihadists have been fighting for more than a decade.

"We urge the Nigerian authorities to thoroughly and impartially investigate all alleged violations of international human rights and international humanitarian law, including deaths and injuries from air force strikes, and hold those found responsible to account," said Magango.

"The government should also provide victims of any unlawful strikes and their families with adequate reparations."