Jihadists attacked a Niger military camp near the border with Mali with artillery and mortars, killing more than 60 people, a security source said on Wednesday.
Tuesday's attack in Inates in the western Tillaberi region was the deadliest on Niger's military since the armed forces began fighting Islamist militants in 2015.
"The attack killed more than 60," the source said. "The terrorists bombarded the camp with shelling and mortars. The explosions from ammunition and fuel were the cause of the heavy toll."
The source did not say which group was responsible for the deadly assault.
Niger forces are fighting against Boko Haram militants in the southeast border with Nigeria and jihadists allied with the Islamic State in the west near Mali and Libya.
Three soldiers and 14 militants were also killed on Monday in an attack on another army post in Agando in western Tahoua region, the defence ministry said.
Heavily armed "terrorists" in a dozen 4x4 vehicles led the attack early Monday morning on the military post in Tahoua, the ministry statement said.
Niger is part of a five-nation anti-jihadist task force known as the G5, set up in 2014 with Burkina Faso, Mali, Mauritania and Chad.
Thousands of civilians and soldiers have died in violence across the vast region, known as the Sahel, which began when armed Islamists revolted in northern Mali in 2012.