In the West African nation of Niger, killings by insurgents have surged since the military seized power in a coup, expelled U.S. and European troops and stopped negotiations with Islamist groups.

Attacks that killed dozens of civilians and soldiers in Niger this month have put a spotlight on the military’s failure to restore security in the West African nation, nearly 18 months after staging a coup.

When the military seized power in July 2023, the generals claimed they were better suited to restore order to a country racked by the world’s deadliest jihadist insurgency. But Niger has since spiraled into further violence, with frequent attacks on military forces, the recent destruction of a village and the killing of more than 20 passengers on a bus.

The Islamic State has claimed responsibility for the attack on military forces. All three attacks took place in western Niger, where affiliates of the Islamic State and Al Qaeda are active.

Militants affiliated with these groups have killed nearly twice as many civilians since the coup, compared with the 18 months that preceded it, according to data from the Armed Conflict Location and Event Data, or A.C.L.E.D., a nonprofit that tracks global conflict.

Since the coup, Niger’s rulers have expelled French military personnel and ordered U.S. armed forces to vacate a sprawling air base in the country’s north. They have turned toward Russia for military assistance, and remained close to Turkey, which has provided drones. The result appears to be a surge of civilian deaths.

“They don’t have a real strategy, except the use of sheer force,” said Rahmane Idrissa, a political scientist from Niger who teaches at Leiden University in the Netherlands.

The country has vowed to strengthen its cooperation with military juntas in neighboring Burkina Faso and Mali by establishing a new security alliance, the Alliance of Sahel States. The three nations are also scheduled to formally pull out of a West African regional bloc known as ECOWAS.

Over the past six months, Niger has recorded the highest number of civilians deaths among the three nations, according to A.C.L.E.D. Niger had been faring better than the other two countries until the government of President Mohamed Bazoum was overtaken during the coup.

A recent report from the United Nations described “the extreme lethality” of the attacks in Niger, most of which have taken place in the western region of Tillabéry, at the border with Burkina Faso and Mali.

Armed assailants killed at least 39 civilians in the two attacks this month, according to government figures. One took place in the village of Libiri, which satellite imagery and videos posted on social media suggested had been burned down. In another attack, the assailants killed civilians traveling on a bus.

An attack in the town of Chatoumane left about 90 soldiers dead, according to security analysts and news reports. The authorities in Niger said that only about 10 soldiers had been killed, though they have regularly underplayed military losses.

A Niger-based security analyst who was briefed on that attack by intelligence services said that the losses were closer to 100 soldiers.

The analyst spoke on condition of anonymity because Niger’s military has cracked down on critics and researchers in recent months. The generals have accused Western news outlets of staging “a campaign of brainwashing” meant to tarnish the country’s reputation. The BBC was suspended from Niger last week for its reporting on the attack in Chatoumane.

On Wednesday, Niger’s national broadcaster said the security situation remained “under control.” Niger’s authorities did not respond to a request to comment.

Security experts say one reason jihadist violence has increased is because Niger’s new leaders ended the talks that Mr. Bazoum had been holding with the insurgents. “Bazoum’s extended hand to those groups was a rare and courageous effort,” said Hannah Rae-Armstrong, an independent researcher who has documented the effects of Mr. Bazoum’s policy, including a drop in civilian casualties in Tillabéry before the coup.

Mr. Bazoum has been held captive in the presidential palace.

Nearly a year after the creation of the Alliance of Sahel States, operational successes have been scarce. Islamist insurgents regularly attack convoys of trucks carrying food and other resources from a port in Togo through neighboring Burkina Faso to Niger’s capital, Niamey.

On Monday, assailants set six trucks on fire in Burkina Faso, according to Niger’s national broadcaster.

“Actual cooperation has been limited because each military is facing its own issues,” said Andrew Lebovich, a researcher at the Clingendael Institute, an organization funded by the Dutch government. “It’s hard to share resources when they’re already stretched thin.”

Hassoumi Sani, a truck driver carrying construction material, said that convoys of up to 400 trucks had to wait for as many as six weeks before Nigerien soldiers could escort them. “With the Nigerien Army, no one is left alone: If a truck breaks down, they’ll haul it to the next city,” he said. On Monday, armed men also attacked an oil pipeline recently inaugurated by a Chinese company.

Kiari Liman-Tinguiri, Niger’s ambassador to the United States under Mr. Bazoum, said of Niger’s military leaders: “The situation is out of their control.”

Christiaan Triebert contributed reporting from New York.