At least 85 civilians were killed in Kaduna state, north-west Nigeria, in an air strike during a Muslim religious celebration on Sunday, the local emergency management authority said.
The civilians were killed in a "bombing mishap", President Bola Tinubu said without giving a death toll.
State Governor Uba Sani had earlier said they were "mistakenly killed" by a military drone "targeting terrorists and bandits".
Dozens were also wounded.
The defence ministry termed the operation a "needless tragedy" adding that a routine mission against militants "inadvertently affected members of the community".
Nigeria's military has for years been battling armed criminals and militants who has been operating in parts of northern Nigeria, raiding villages and kidnapping residents for ransom.
Defence spokesman Maj Gen Edward Buba said Sunday's airstrike was based on credible intelligence about the presence of "terrorists" in the area.
President Tinubu has asked for a "thorough and full-fledged investigation into the incident and calls for calm while the authorities look diligently into the mishap" a statement from his office said. The governor has also called for an investigation.