Col. Moustapha Michel Ledru said today that three soldiers were also wounded in fighting in the Diffa region between Niger's military and the Nigeria-based Islamic extremists.
He said the Boko Haram fighters retreated after the military fought back, taking arms and ammunition from the extremists.
Thousands of people fleeing Boko Haram attacks have fled to the Diffa region in Niger.
Boko Haram's nearly seven-year insurgency has killed thousands and displaced millions. The extremists have been launching attacks across Nigeria's borders into Niger, Chad and Cameroon. Those countries are contributing to a multinational force fighting Boko Haram.