Some 71 Nigerien fighters were killed at a military camp near Inates on Tuesday, with another 12 people - believed to be the attackers - also dead.
The attack comes at the end of a year of intense violence in Inates, a cattle herding community near the banks of the Niger River 200 km north of the capital Niamey. Apart from the casualties, the ministry, in a televised statement, confirmed that few military personnel are unaccounted for.
"The terrorists bombarded the camp with shells and mortars".
The source did not say which group was responsible for the deadly assault.
The Defense Ministry said reinforcements had been deployed to the area and the situation on Wednesday was "under control".
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It said the tax was "unusually burdensome" for United States companies including Alphabet's Google, Facebook, Apple and Amazon. He also noted that France will reimburse the tax if the US agrees to the worldwide tax plan.
Tuesday's attack prompted French President Emmanuel Macron to postpone a meeting scheduled for next week in the southwestern French town of Pau, where he and five presidents from the Sahel were due to discuss security in the region. The event, which aimed to address security in the volatile region, is now expected to take place early next year.
President Mahamadou Issoufou of Niger has raced to home to deal with a deadliest rebel attack on his country in living memory.
That is in addition to the thousands of civilians who have died, and more than a million who have been displaced since the jihadist revolt began in Mali in 2012.
The conflict has since spread to the centre of Mali and to neighbouring Burkina Faso and Niger.
The G5 Sahel force, which France is backing in the hope that it will help it to draw down its own troops in the region, is struggling from funding problems, shoddy or outmoded equipment and poor training.
Two of the sources said another 30 soldiers had been wounded.