The attack happened on Sunday at approximately 3pm (14:00 GMT), when the unidentified assailants arrived at the village of Wiye in the Banibangou district, about 50km (30 miles) from the border with Mali.
One person who was wounded had been evacuated for treatment in the capital, Niamey, it added.
Security measures had been stepped up and an investigation was under way to identify and bring to trial those responsible for “these cowardly and barbaric attacks”, it said.
There has been no claim of responsibility so far.
Banibangou falls inside what is known as the three-borders region between Niger, Burkina Faso and Mali, which for years has been the scene of bloody attacks by armed groups linked to al-Qaeda and ISIL (ISIS).
Previous attacks in Niger’s western Tillabery region have been attributed by local officials to an affiliate of ISIL, including raids in January that killed at least 100 civilians.
In mid-March, an attack in the same district targeting a village market left 66 people dead, while on June 24, attacks on villages in Tondikiwindi, in a neighbouring district, killed 19 people.
Despite repeated efforts by the authorities to secure the region, violence has continued, often carried out by gunmen on motorbikes who flee across the border into Mali after their raids.
A contingent of 1,200 Chadian soldiers is deployed in the three-borders region as part of a multinational force put together by the G5 Sahel group, which comprises Burkina Faso, Chad, Mali, Mauritania and Niger.