Suspected Islamist militants killed 25 soldiers and wounded six in an attack on an army post in west Niger near the Mali border, government said.
It was not immediately clear who was responsible for the attack on the post at Chinagodrar, north of Niamey.
It coincides with a campaign by Islamist groups connected to al Qaeda and Islamic State to force the Nigerian army back from its western frontier with Mali, where government control of the rural centre and north has all but evaporated because of jihadists.
Attackers approached the military post on motorcycles and in other vehicles and were met with resistance from the army and the air force, government said in a statement. Sixty-three assailants were killed.
“The Defence ministry offers condolences to the victims and wishes the wounded a prompt recovery,” the statement said, adding a search operation was underway to find those responsible.
Despite efforts by international forces, attacks have risen four-fold over the past year in Niger, killing nearly 400 people, according to data from the Armed Conflict Location and Event Data Project, a non-profit research organisation.
They include a raid last month that killed 71 soldiers at another military outpost west of Chinagodrar, believed to be the biggest attack on the Nigerian military.
Security deteriorated this year across the Sahel amid jihadist attacks and deadly ethnic reprisals between rival farming and herding communities.