The 55 "neutralized terrorists" include several senior military operatives as well as several religious leaders, the Niger military said, using a traditional term for jihadists.
The figures were given in an army bulletin on operations in Niger's southeastern region of Diffa, seen by AFP on Monday.
The 22-day operation which ended Sunday targeted an Islamic State West Africa Province (ISWAP) stronghold in Arege in northeastern Nigeria's border region with Niger, it said.
The ground and air operation aimed to "maintain pressure" on ISWAP and cut supply routes, the bulletin added.
Two soldiers were killed and three were injured, it said, adding that 13 vehicles, 13 motorcycles and five "booby-trapped vehicles" were destroyed.
Niger earlier this month said the army had picked up nearly 1,400 Boko Haram followers who were fleeing into the country following clashes with ISWAP.
The exodus started in March when ISWAP pursued Boko Haram in its forest hideout of Sambisa in northeastern Nigeria.
Niger's Diffa region has born the brunt of jihadist attacks over the years but has been relatively calm since the start of 2023, a security source told AFP.
The vast Lake Chad region, shared by Nigeria, Niger, Cameroon and Chad, is a notorious locus for Boko Haram jihadists and ISWAP, their deadly rival.
Niger, one of the poorest nations in the world, is also facing a jihadist insurgency in its southwest, launched by militants who launched cross-border raids from Mali in 2015.
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