Eleven Nigerien security personnel died in an ambush against a regional prefect's motorcade near the country's border with Burkina Faso on Wednesday, the interior ministry said on Friday.
The ministry's toll was higher than the deaths reported by local officials.
It is part of the "tri-border" zone between Niger, Burkina Faso and Mali, known for high levels of attacks by jihadists linked to Al Qaeda and the Islamic State group (IS), especially against civilians.
The ministry said in a statement that 10 National Guard personnel and one gendarme "fell on the field of honour", adding that three more people had been wounded.
Two National Guard vehicles were burnt and another damaged by the unidentified assailants, who used rifles and rocket launchers, the ministry said.
"An investigation is under way to find and bring to justice the perpetrators of this criminal attack," the statement added.