The assailants ambushed a supply mission at 1100 local time in Torodi commune after which soldiers evacuating the wounded hit an improvised explosive, the ministry said late on Sunday, Reuters reported.
"We regret that unfortunately 15 soldiers were killed, seven were wounded and six are missing," it said.
Like its neighbours Mali and Burkina Faso, Niger is a regular target for militant groups linked to al Qaeda and ISIL, which have grown stronger despite the deployment of thousands of regional, Western and UN troops across West Africa's Sahel region.
ZZ/PR