An army statement said the attack took place on Friday afternoon, targeting "a group of paramilitary police escorting a convoy" along a road near the border with Burkina Faso.
The statement said five people had been killed and 19 injured, including seven officers, five soldiers, and seven civilians, who were all taken to the capital Niamey.
"On the side of the enemy, two terrorists were killed," said the statement.
The attack took place in the southwestern Tillaberi region, in the border area where Niger, Burkina Faso and Mali meet – a hotbed of activity for insurgents linked to Al-Qaeda* and the Islamic State* group.
The vast arid area, roughly the size of South Korea, has around 150,000 internally displaced people, according to the UN.
On Wednesday, the UN and local authorities said nearly 11,000 had fled their homes this month alone.
One of the poorest countries in the world, Niger is also struggling with jihadist violence that has spilled into its southeast from northeastern Nigeria.
* al-Qaeda and Daesh (ISIL/ ISIS/ IS) are terrorist groups banned in Russia and many other countries