At least 36 soldiers were killed in Nigeria's northcentral region this week during an ambush by armed gangs and in the crash of a helicopter sent to the scene, the military said Thursday.

The helicopter was shot down by the armed gangs in Niger state’s Wushishi district following clashes earlier in the week, residents told the Associated Press (AP), echoing warnings from analysts about the growing might of the gunmen in the country's hard-hit northern region.

Gangs of heavily armed men have wreaked havoc across northwest Nigeria in the past two years, kidnapping thousands, killing hundreds and making it unsafe to travel by road or to farm in some areas.

Soldiers were conducting an "offensive operation" in Niger state on Monday when they were ambushed by the armed gangs, defense spokesman Maj. Gen. Edward Buba told reporters.

"The ambush and the firefight resulted in the death of three officers, 22 soldiers," he said, adding that seven soldiers were wounded.

An Air Force Mi-171 was then sent to evacuate the casualties but it crashed in another part of the state, resulting in the death of 14 additional military personnel including the pilots and crew members, Buba said.

He said the reason for the crash is being investigated.

Thousands of Nigerians have been killed in the last year by the armed gangs which mostly comprise former herdsmen who have taken up arms after clashing with farming communities for several decades over limited access to land and water.

The defense spokesman said several other operations had left dozens of gang members either killed or in custody, and said that the security forces remain committed to restoring peace in violent hotspots.

The attack adds to other challenges confronting Nigeria’s President Bola Tinubu, who is leading efforts by the West Africa regional bloc of ECOWAS – which he chairs – to restore democracy in Niger after the recent coup.