The attack took place in the militancy-hit border region of Niger, Burkina Faso and Mali.
Niger has declared 48 hours of national mourning after 37 people were killed in a fresh massacre by suspected militants.
"Flags will be flown at half-mast across the country" with immediate effect, a government statement said.
It reaffirmed the government's determination to "pursue the fight against terrorism until the final victory", urging greater vigilance among the population.
Gunmen on motorbikes launched an attack on villagers Monday in Darey-Daye as they were tending their fields. Four women and 13 children were among the 37 people killed.
The massacre bore the hallmarks of extremist attacks that have battered western Niger since 2015, when an armed militant campaign spread from Mali.
Darey-Daye, which was hit in an attack in March that claimed 66 lives, lies in the Tillaberi region, which has borne the brunt of the bloodshed.
The village is located in the department of Banibangou, in the so-called "tri-border" area where the frontiers of Niger, Burkina Faso and Mali converge.
As we rightly fear atrocities as the Taliban takes over Afghanistan, Islamist groups are already killing in Africa’s #Sahel: 37 dead in 16 Aug IS attack in Niger, and 51 more in Mali days earlier = 700+ civilians killed in Sahel by IS/AQ in 2021. https://t.co/MhSaShxWf9— Corinne Dufka (@CorinneDufka) August 17, 2021
The area is notorious for attacks by highly mobile terrorists linked to Al-Qaeda.
According to a toll issued last week by Human Rights Watch, more than 420 civilians have been killed in extremist attacks in Tillaberi and the neighbouring region of Tahoua this year, and tens of thousands of people have fled their homes.