NIAMEY, Niger—The jihadists came at night on motorcycles and surrounded a remote village on Burkina Faso’s eastern border with Niger. By the early hours of Saturday morning, over 130 civilians were confirmed dead by the government—the worst terrorist atrocity in the history of a country that has been plunged into extremist violence in recent years—prompting calls to intensify international counterterror efforts across West Africa.

During the three-hour onslaught on Yagha village, the militants shot indiscriminately, torching homes and a market before lobbing explosives at civilians seeking refuge in gold-mining holes, according to government officials and nongovernmental organizations based in the region. No one has claimed the killings, but government officials say it was the work of Islamic State’s regional affiliate, the Islamic State in the Greater Sahara, or ISGS, which has killed hundreds of civilians in recent months.

Amed, a gold-miner from Yagha, said he was woken up by the sound of Kalashnikovs. He survived by hiding in a mining hole the Jihadists didn’t discover. “I found the bodies of four of my friends and we buried them in a mass grave,” he said over phone. “When our army says it’s safe, I don’t know what they mean,” he said.

Roch Kabore, the country’s president, decreed a three-day national mourning period. “I bow before the memory of the hundred civilians killed in this barbaric attack,” he said in a televised address.

António Guterres, United Nations’ secretary-general, said the “heinous attack” underscored the “urgent need for the international community to redouble support to Member States in the fight against violent extremism.” The State Department condemned the attack, stressing that it “stands with Burkinabe partners in the fight against violent extremism.”

The atrocity, the deadliest since jihadist attacks first hit Burkina Faso in 2015, is rekindling concerns that the West and its local allies are losing the battle against Islamists in the impoverished nations of Sahel—a 3,000-mile semiarid territory on the southern shore of the Sahara encompassing Mali, Niger, Burkina Faso, Ivory Coast and Chad—after largely defeating them in the Middle East.

Burkina Faso is facing a swelling insurgency spawned from several Islamic State and al Qaeda affiliates that has pushed some 1.2 million people from their homes in what the U.N. calls the world’s fastest-growing displacement crisis. Neighboring Niger is fighting militant armies on multiple borders. Chad is witnessing the spillover from Islamic State West Africa’s expansion in Nigeria, where it controls hundreds of miles of territory and is taxing and subsidizing local farmers. Militants in northern Mali, armed with weapons smuggled out of chaotic Libya, are attacking U.N. peacekeepers.

French soldiers on patrol in norther Burkina Faso in 2019. France has some 5,000 troops in the region.

French soldiers on patrol in norther Burkina Faso in 2019. France has some 5,000 troops in the region.

Photo: michele cattani/Agence France-Presse/Getty Images

In recent months, local franchises of Islamic State and al Qaeda, which are seeking to overturn Western-allied governments, have executed hundreds of tribal chiefs and civil servants in the so-called tri-state region where Burkina Faso, Niger and Mali meet, forcing their families to swear allegiance. These local affiliates, ISGS, and the al Qaeda coalition, Jama’at Nusrat al-Islam wal Muslimin, or JNIM, have even started fighting each other. The escalation of violence has caused about 8,000 fatalities, between 2015 and 2020, most of them in Burkina Faso, according to the Pentagon’s Africa Center for Strategic Studies. Last year, Burkina Faso’s government armed hundreds of volunteer militiamen to aid the army, but the jihadists have responded by killing whole communities deemed to support the vigilantes.

“The attack underscores the ongoing challenges of the regional fight against jihadists who continue to exploit the porosity of the frontiers and the overextension of security forces,” said J. Peter Pham, former U.S. Special Envoy for the Sahel, now with the Atlantic Council, a Washington-based think tank.

After losing its caliphate in Syria and Iraq following the U.S.-led military campaign, Islamic State has made significant headway in Africa, from northeastern Nigeria, where its local franchise controls hundreds of miles of territory, to Congo and northern Mozambique where it is threatening a $16 billion natural-gas project.

In response, the U.S. has boosted intelligence sharing with France—the former colonial power in West Africa which has some 5,000 troops in the region—providing aerial surveillance from drones flying out of a new $110 million air base in northern Niger. Both countries have military bases in Burkina Faso’s capital Ouagadougou, hundreds of kilometers to the south of this weekend’s atrocity.

The Trump administration had signaled it would dramatically reduce the U.S. military footprint in Africa—more than 6,000 troops and civilians concentrated in Niger in the west and in Somalia and Djibouti in the east—but didn’t follow through and the Biden administration has said little about that goal.

“This attack confirms the inadequacy of counterterrorism policies as governments—trained and backed by international forces—are unable to protect civilian populations against extremely nimble groups,” said Virginie Baudais, in charge of Sahel policy analysis at the Stockholm International Peace Research Institute, a conflict-resolution think tank.

On Friday evening, hours before the Solhan attack, gunmen killed 13 civilians and a soldier in Tadaryat, another village in the region, say Western security officials. In March, jihadists killed 137 villagers in Niger’s southerwestern region of Tahoua, the deadliest by suspected jihadists in the country’s history. A month later, militants ambushed and executed two Spanish journalists and an Irish conservationist on an anti-poaching mission.

During the Solhan rampage, government-backed militiamen were outgunned and unable to stop the killings, said local human-rights activists. The army, based 15 kilometers away, arrived one hour after the attackers had left. On Sunday, local hospitals were struggling to treat dozens of wounded. “We ask all available health staff to go to the regional hospital to lend a hand to colleagues,” said the health facility in the nearby town of Dori. “We also invite those who can donate blood to do so, to save lives.”

Local activists said the ISGS faction is known for perpetrating massacres in villages that refuse to pledge loyalty. Solhan is an artisanal gold mining site, whose revenue stream is coveted by the jihadists.

One regional ISGS commander, Abdelhakim al-Sahrawi, has been nicknamed the butcher for beheading local chiefs with his own hands, said a former counterterrorism official in neighboring Niger. But Niger’s Foreign Minister Hassoumi Massaoudou said the violence against unarmed targets may be evidence the armed groups are on a backfoot. Rather than the army, “these terrorists are attacking civilian populations. That’s proof they are weakening,” he said in an interview.

Write to Benoit Faucon at benoit.faucon@wsj.com and Joe Parkinson at joe.parkinson@wsj.com