But the ministry did not say which group was responsible.

The attack is one of the deadliest since soldiers seized power in a military coup in the country in July.

Niger, like neighbours Mali and Burkina Faso, is battling militants linked to al Qaeda and Islamic State that have killed thousands and displaced over two million people in the West Africa Sahel region.

The defence ministry said the soldiers were returning from operations against the militants when they were targeted by over 100 assailants in vehicles and on motor-bikes using explosive devices and suicide bombers.

Three days of national mourning has been declared, the statement said.