Niger says 23 of its soldiers have been killed in a "terrorist" ambush near the borders with Burkina Faso and Mali in a western region prone to militant attacks.
Niger is ruled by military leaders who seized power in a July coup, citing a worsening security situation as justification for the power grab.
But an insurgency that had already gone on for eight years has continued.
In the latest bout, Nigerien soldiers were engaged in a security sweep in Tillaberi, in the three borders area, on Tuesday and Wednesday, the defence ministry said late Thursday.
They were killed during a "complex ambush", it said, adding that "about 30 terrorists had been neutralised".
'Reassure people'
The army raids were "designed to reassure local people" who were being targeted by armed groups engaged in "murders, extortion and cattle rustling", the ministry said.
More than 100 "terrorists" in vehicles and on motorbikes attacked the army unit between Teguey and Bankilare using "home-made bombs and suicide vehicles".
In addition to the 23 soldiers who died, 17 were wounded.
Three days of national mourning began Friday, according to a statement read on state television.
Tillaberi borders Burkina Faso and Mali - also under military regimes - in a region plagued by insurgent attacks.
Al-Qaeda links
Groups linked to Al-Qaeda and the Daesh terror grouo have operated in Tillaberi since 2017 despite a massive deployment of anti-insurgent forces.
In January, 22 civilians were killed in an attack on the Tillaberi village of Motogatta, about 100 kilometres (60 miles) north of the capital Niamey.
Niger, one of the world's poorest countries, had been a frontline partner of the West in battling insurgents in the Sahel.
But after seizing power, the junta, led by General Abdourahamane Tiani, kicked out forces from former colonial power France, whose 1,500 troops had left Niger by the end of last year.
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