The government of Niger said on Monday that militants killed 137 people in coordinated raids on villages in the south-west of the country on Sunday.
The announcement is an amendment to the previous toll, which put the death toll at 60, according to local authorities.
This comes less than a week after unidentified gunmen killed 58 villagers in the same area.
Government spokesman Zakaria Abdel Rahman said the government strongly condemned the systematic terrorism against civilians.
In a statement on state television, he said that the government had declared three days of public mourning, and would “take decisions to counter the terrorism of these armed gangs”.
Earlier in the day, a resident told AFP by telephone that a first attack “took place in the afternoon [on Monday] and targeted a bus carrying passengers in the Panipango-Shinigodar area” in the Tillabéry region, adding that the attack had killed “about 20 people”.
Tillabéry region, located in the border triangle between Niger, Burkina Faso and Mali, has been the scene of bloody attacks by takfiri groups linked to al-Qaeda and ISIS for years.