Scores of people have died in the deadliest suspected terrorist massacre ever to hit Niger, the government said Monday, underscoring the huge security challenge facing new President Mohamed Bazoum.

Government Spokesperson Zakaria Abdourahamane said 137 people had died in Sunday's raids in villages near Niger's border with Mali.

"In treating civilian populations systematically as targets now, these armed bandits have gone a step further into horror and brutality," Abdourahamane said in a statement read on public television.

Announcing three days of national mourning for the victims from Tuesday, he vowed that the government would reinforce security in the region and bring "the perpetrators of these cowardly and criminal acts" to justice.

Gunmen arriving on motorbikes attacked the villages of Intazayene, Bakorat and Wistane on Sunday, shooting "at everything which moved," a local official said. The jump in the death toll, which had been given as at least 60 earlier Monday, would make Sunday's attacks the deadliest ever committed by suspected terrorist groups in Niger. It brings the number of fatalities in the Mali-Niger border region to 236 in just over a week.

The world's poorest nation according to the United Nation's development rankings for 189 countries, Niger is also struggling with insurgencies that have spilled over from Mali and Nigeria. Hundreds of lives have been lost, nearly half a million people have fled their homes and devastating damage has been inflicted in the former French colony.

The three villages are located in the arid Tahoua region in western Niger, abutting the Tillaberi region in a border zone notorious for terrorist attacks. On March 15, a suspected terrorist killed 66 people in the Tillaberi region, attacking a bus carrying shoppers from the market town of Banibangou, and then raided the village of Darey-Daye, killing inhabitants and torching grain stores.

The same day, an attack claimed by the Daesh group in the so-called "tri-border area" where the frontiers of Niger, Burkina Faso and Mali converge left 33 Malian soldiers dead.

"After the Banibangou massacre, yesterday the terrorists, in the same barbaric way, struck the peaceful civilian populations of Intazayene and Bakorat," Bazoum said in a tweet on Monday, offering "heartfelt condolences to the victims' relatives."

Bazoum's election was confirmed on Sunday by the poor Sahel nation's constitutional court. On Jan. 2, 100 people were killed in attacks on two villages in the Mangaize district of Tillaberi.

The massacre, one of the worst in Niger's history, occurred between two rounds of the country's presidential election. A year earlier, on Jan. 9, 2020, the Niger army lost 89 men in an attack on a military camp in Chinegodar, one month after 71 troops died in an attack at Inates.

Bazoum, elected on Feb. 21, is a former interior minister who was the preferred successor and right-hand man of outgoing president Mahamadou Issoufou. He has vowed to fight insecurity and ordered army reinforcements to the Tillaberi region after the bloodletting of March 15.

Turkey on Monday condemned the deadly terrorist attacks in northwestern Niger.

"We are deeply saddened that at least 40 people lost their lives in the terrorist attacks carried out on 21 March 2021, in settlements located in the Tillia city of Tahoua region, in Niger," the Foreign Ministry said in a statement. "We strongly condemn this heinous attack."

It extended condolences to the families of those who lost their lives, as well as to the "friendly and brotherly" people and the government of Niger.