About 70 soldiers have been killed in an attack on a military camp in Niger near the border with Mali, four security sources have told Reuters.
It is believed to be the deadliest raid against the Nigerien military in living memory.
Islamist militants have mounted increasingly lethal attacks across West Africa's Sahel region this year despite the commitment of thousands of regional and foreign troops to counter them.
Tuesday night's attack targeted a base in the western town of Inates, the sources said, near where Islamic State's West African branch killed nearly 50 Nigerien soldiers in two attacks in May and July.
Niger's President Mahamadou Issoufou. Source: DPA
Two of the sources said another 30 soldiers had been wounded.
Nigerien authorities were not immediately available to comment and details on the attack were limited.
President Mahamadou Issoufou's office tweeted that Issoufou had cut short a visit to Egypt in order to return to Niger "following the tragedy that occurred in Inates".
