Seven soldiers have been killed in southwestern Niger in an attack by suspected militants, and five others died in a traffic accident while trying to respond to the assault, the country's defence minister said.

A military unit was "violently attacked by several hundred terrorists" in the town of Kandadji, Salifou Mody said in a statement on Thursday, adding that seven soldiers were killed in the fighting.

"During an intervention" launched in response to the attack, "a tragic traffic accident led to the loss of five of our brave soldiers", he continued.

Another seven people were wounded and evacuated to a hospital, he said.

"A hundred terrorists, their motorcycles and [their] weapons were destroyed" about 20 kilometres northeast of Ayorou in the same region, the minister said.

"A search and sweep operation is now under way in order to track down the enemy."

Three-border zone

The Tillaberi region, where the attack took place, is located in the so-called "three borders" zone where Niger, Burkina Faso and Mali meet.

The area is a hideout for militants, particularly those affiliated with Daesh in the Greater Sahara.

Niger's elected government was toppled in late July by a coup whose leaders cited the deterioration of the security situation in the country as justification.