"Nobody attacks Niger without punishment and Boko Haram learned that to its cost last February 6," Issoufou told a crowd after a rally in the capital Niamey. "That day, our defence and security forces crushed Boko Haram."
The radical sect struck across the border into Niger for the first time on February 6, launching attacks on Bosso and near provincial capital Diffa, both southeastern towns near Nigeria.
A first official toll given by Defence Minister Mahamadou Karidjo said 109 jihadists had been killed, with four soldiers and a civilian. Niger's army later said that more than 200 Boko Haram fighters were slain, while seven soldiers perished.
"Niger will be the tomb of Boko Haram," Issoufou said to heated applause from the crowd who had marched through Niamey in a protest called by the ruling party and joined by civic bodies.
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Earlier, Prime Minister Brigi Rafini led the marchers under a heavy police presence, with snipers posted on roofs of buildings along the protest route, including parliament.
"Boko Haram is itself haram (forbidden)," read one sign, referring to the name of the jihadist group, which roughly translates as "Western education is forbidden."
Muslims in Niger who were previously "troubled, waiting to see, are now free to say no to Boko Haram," he added.
"Our army, our pride," read one of the many signs -- sometimes daubed in the green, white and orange national colours -- after the army joined the regional fight against the brutal sect.
Boko Haram has waged an insurgency aiming to create a hardline Islamic state in northeast Nigeria since 2009, a conflict that has claimed some 13,000 lives.