NDJAMENA, Chad — In an unusual joint counterterrorism operation recently, troops from Mali, Mauritania and France seized a large cache of weapons and ammunition from a suspected Qaeda camp in a forested area along the border of the two African countries.

The raid provided a glimpse of an expanding and often violent multifront campaign that France has joined here in the Sahel, a vast area on the southern flank of the Sahara that stretches from Senegal to Sudan. Over the past several years, French troops have battled Al Qaeda’s North Africa affiliate and other Islamist extremists in Mali, and have helped African troops thwart Boko Haram, a violent militancy that has spilled from Nigeria to attack Chad, Niger and Cameroon. The Islamic State is also a looming threat.

In the latest sign of an emerging regional collaboration, five countries within the Sahel — Mauritania, Mali, Burkina Faso, Niger and Chad — announced recently that they would create three border areas for military patrols and operations. French troops are advising and assisting these units.

The Trump administration, which is already fighting the Islamic State in both Iraq and Syria and weighing whether to send several thousand more American troops to Afghanistan to fight the Taliban, has been only too eager to continue Obama-era policies of providing financial, logistical and intelligence support to France in this region. By doing so, it hopes to avoid having to put American combat forces on the ground in yet another global hot spot.

American and French officials say their close military and counterterrorism partnership will continue unchanged after the election last week of Emmanuel Macron as France’s next president.

 

“I have no doubt that the French will continue to make their own decisions in their own best interest and that the terrorists will not enjoy these decisions,” Defense Secretary Jim Mattis said last month during a visit to Djibouti, home to the Pentagon’s only permanent military base on the African continent.

Three years ago, France reorganized its 4,000-member force in West Africa to more effectively carry out its counterterrorism fight, called Operation Barkhane, in some of the harshest terrain on the planet.

The French military has concentrated its air power, including three Mirage fighter jets, and mission headquarters here in Chad; its five Reaper reconnaissance drones in Niger; its special operations troops in Burkina Faso; and its logistics hub in Ivory Coast.

As an example of the growing cooperation between the Pentagon and France, an American military planner will, for the first time, join the headquarters staff of the French operational command.

Having France, with its deep cultural and historical ties to the region, take the lead in counterterrorism operations here saves the United States from having to assume another major military mission. For France, the Pentagon’s aerial refueling, transportation and intelligence assistance are crucial to the operation’s success.

“Not only would that be more expensive than helping the French, but the fact of the matter is that the French are better at operating in that part of the world,” said Michael R. Shurkin, a senior political scientist at RAND and a former analyst for the Central Intelligence Agency. “As for U.S. aid to the French, the stark reality for the French is that they simply could not operate there without our help.”

But it is a risky mission for French troops and their African allies, as the departing French defense minister, Jean-Yves Le Drian, said while visiting troops in Mali, Niger and Chad in February. Mr. Le Drian cited the expanding support and partnerships with regional forces and noted the terrorist threats that plague these desperately poor countries, which have difficulty enforcing their loosely guarded borders against extremists.

“Unfortunately, our fight against jihadist groups is not a fight against a regular army,” Mr. Le Drian said in Niamey, Niger’s capital. “Whatever your success on the ground, it does not protect us from an attack.”

Mali is perhaps the most striking illustration of that chaos. In 2012, Mali’s north fell under the control of Qaeda-linked jihadist groups who hijacked an ethnic Tuareg-led rebel uprising, though the Islamists were largely ousted by a French-led military operation in January 2013.

But militants continue to roam the country’s north and center, mounting attacks on civilians and the army, as well as French and United Nations forces still stationed there. A suicide bomber in a vehicle filled with explosives led an attack on a military camp in northern Mali on Jan. 18, killing at least 60 people.

 

Many of the casualties were soldiers and former fighters who reached a peace agreement with the government in 2015 and had been working together to try to stabilize the region.

The attack dealt a setback to peace efforts in northern Mali, underscoring the magnitude of the challenges that remain four years after the French-led military intervention to drive militants from power in the region’s major towns. The peace agreement that followed has proved difficult to carry out.

“Mali is worse than ever. I’m very pessimistic,” said Mr. Shurkin, the political scientist. “I put the blame on the Malian state, which needs to be in crisis mode. Yet as far as I can tell, it appears to be carrying on as if nothing bad was happening, or as if Mali’s international partners were taking care of all the problems. But they’re not.”

In April, a French soldier was killed in Mali after a clash with armed militants.

Gen. Thomas D. Waldhauser, the head of the Pentagon’s Africa Command, noted France’s sacrifices and commitments to the region and praised the French role. “We look for our partners in that part of the continent to really carry the fight there,” General Waldhauser said during the same visit to Djibouti as Mr. Mattis.