At least a dozen Nigerien soldiers were killed following an attack by hundreds of armed insurgents on motorbikes, the defence ministry said.
The attack happened at about 190 km from the capital Niamey in Kandadji, near the tri-border zone of Mali, Burkina Faso and Niger on Thursday morning.
The area has been the epicenter of Islamist insurgencies in the Sahel region in the last few years.
Seven soldiers were killed in combat while five others died in an accident while driving to reinforce the unit that had come under attack, the statement said.
Earlier on Thursday, three sources including a senior military officer, said at least ten soldiers were killed.
Neither the sources nor the defence ministry say which group was responsible. Local affiliates of al Qaeda and Islamic State are active in the region and wage frequent attacks on soldiers and civilians.
The defence ministry statement said around a hundred insurgents were killed and their motorbikes and arms were destroyed. It gave no further details.
Two security sources said the army responded to the attack with ground troops as well as helicopters, one of which was hit but was able to return to its base.
Niger is run by a military junta that seized power in a coup in July, partly out of discontent at the worsening security situation.
Neighbouring Mali and Burkina Faso have each had two coups in the last three years.
However, security analysts say attacks had been falling in Niger under ousted President Mohamed Bazoum, who had tried to engage with Islamists and the rural communities where they are rooted.
At least 17 soldiers were killed in another attack in southwestern Niger in mid-August.
France said on Sunday it would withdraw its 1,500 troops from Niger before the end of the year, after weeks of pressure from the junta and popular demonstrations against the former colonial ruler, which had forces there to fight the insurgents.
On Thursday, several hundred pro-junta supporters gathered again in front of the French military base in Niamey to demand that the troops leave immediately.
