DAKAR, Senegal — Even before France announced Wednesday that its forces had killed the leader of the Islamic State in the Greater Sahara, the terrorist group appeared to be struggling.
The group that once used to carry out major attacks on military bases in Niger and Mali, and in 2017 killed four U.S. soldiers and five of their Nigerien partners, has lately been reduced to massacring defenseless villagers.
In announcing the death of the group’s leader, Adnan Abu Walid al-Sahraoui, the French president, Emmanuel Macron, declared it “another major success in our fight against terrorist groups in the Sahel.”
It may be a blow from which I.S.G.S., as the group is known, cannot recover, especially given the French military’s claim in July that it had killed two of its other leaders, both also surnamed al-Sahraoui. But that is uncertain.
“It’s unclear to what extent the leadership structure is irrevocably damaged,” said Hannah Armstrong, senior analyst for the Sahel region at the International Crisis Group. “They’ve definitely cut off the head and the chest.”
Mr. al-Sahraoui created I.S.G.S. with a band of followers in 2015, pledging allegiance to the Islamic State in Iraq and the Levant. The militants carried out many deadly raids on security forces in the border between Mali and Niger, two vast countries of the Sahel, as the arid band south of the Sahara is known.
But the outfit recently lost much of its power in the face of French airstrikes, as well as from clashes with rival jihadist groups. In January, French and Malian forces killed about 100 jihadists in central Mali, though it was not clear from which group or groups. Several terrorist groups operate in the region.
Some experts cautioned against broad pronouncements of victory.
“It’s not the first time a key leader is killed and yet the group continues to exist and continues to expand,” said Rida Lyammouri, a senior fellow at the Policy Center for the New South, a Moroccan think tank. “Success should be measured by the group not being able to terrorize civilians — not only the military — and by the displaced population returning to their villages. It’s premature to call it a success.”
The United States provided some general intelligence to French officials to help track Mr. al-Sahraoui, an American military official said on Thursday.
Some analysts have questioned the French strategy of aiming to take out top jihadist leaders, arguing that new leaders — sometimes, even more violent ones — can spring up to fill the vacuum.
This is a point that France’s defense minister, Florence Parly, addressed in a statement about Mr. al-Sahraoui’s killing that was broadcast on French television.
“We often hear about the hydra of terrorism,” she said. “If the death of the emir of I.S.G.S. is important, it is because it is the culmination of a long series of neutralizations and captures which disorganized and divided the high command of the organization.”
Ms. Parly, using an alternative name for the Islamic State, said: “The death of Adnan Abu Walid al-Sahraoui is a decisive blow to Daesh’s command in the Sahel, but also to its cohesion. Because I.S.G.S. will undoubtedly have difficulty replacing its emir with a figure of the same stature.”
Mr. al-Sahraoui was thought to come from Western Sahara, a disputed territory that has rejected Morocco’s claims of sovereignty over it, and he is believed to have attended college in Algeria before moving to Mali.
There, with several other jihadists, he founded the Movement for Unity and Jihad in West Africa, known as Mujao, in 2011. After an uprising and coup in Mali in 2012, he became one of the rulers of the city of Gao, imposing Shariah law.
Those who knew him at that time recall him as the intellectual, “the thinking head” of Mujao. But in 2015, he broke away and threw in his lot with the Islamic State.
As Mr. al-Sahraoui recruited from Fulani communities, exploiting their grievances against the state, the group quickly grew in strength.
When his troops ambushed a patrol of U.S. and Nigerien soldiers in Tongo Tongo, in the Tillabéri region of Niger, the group captured global attention.
Typically, hordes of fighters on motorcycles used to swarm in and overwhelm military targets, killing dozens of soldiers at a time, stealing their weapons and then disappearing back into the desert.
But in 2020, the group’s fortunes fell.
Over that year, an estimated 400 to 500 of its fighters were killed by French strikes and in battles with a group aligned with Al Qaeda, Jama’at Nusratul Islam wal Muslimin. The following year, they increasingly turned their guns on civilians, killing over 100 villagers in an attack in January and 58 men returning from a trade fair in March.
“These massacres should be seen as a sign of weakness, not strength,” Ms. Armstrong said. “They’re killing farmers, not soldiers.”
Civilians in Niger have responded to the violence by trying to set up vigilante groups, reflecting a pattern across the wider region that often leads to interethnic tensions and indiscriminate violence.
The French now appear poised to try a somewhat different approach.
They have announced that early 2022 will see the end of Operation Barkhane, their military mission in the Sahel, which has about 5,000 troops in the region. The focus will now be on Takuba, an international task force in which thousands of French soldiers are expected to take part.
France, along with Germany, which also has some forces in the Sahel, has reacted angrily to reports that Mali is considering a deal with a Russian mercenary group, Wagner, to provide it with soldiers.
On Wednesday, France released more details about the killing of Mr. al-Sahraoui. The government said he was killed in Mali toward the end of August, in an operation that involved a commando group backed by air support.
Mr. Lyammouri pointed out that the French announcement about Mr. al-Sahraoui’s death came long after Malians had reported it. The timing, he suggested, may have something to do with the possible Wagner deal.
“It took them about a month to claim it,” Mr. Lyammouri said. “Why wait this long?”
Eric Schmitt contributed reporting and Mady Camara contributed research.