DIFFA, Niger » Across Africa, affiliates of al-Qaida and other Islamist militants are proving resilient and in some cases expanding their influence, from Nigeria to Libya to Somalia, Western and African counterterrorism officials say.

So it is not surprising that the authorities in this poor West African desert nation, which has emerged as a staunch ally of France and the United States in the fight against Islamist militancy, are nervously watching Boko Haram, a sect in neighboring Nigeria suspected of killing more than 400 civilians in the past five weeks alone, including children watching a soccer match over the weekend.

Officials say the group’s fighters have made a habit of quietly slipping across the border into Niger to rest, rearm and refit — a pipeline the nation is eager to shut down with the Pentagon’s help. But instead of launching U.S. airstrikes or commando raids on militants, the latest joint mission between the nations involves something else entirely: U.S. boxes of donated vitamins, prenatal medicines and mosquito netting to combat malaria.

With more than a decade of land wars in Iraq and Afghanistan drawing to an end, the U.S. military’s involvement in Niger illustrates how the Pentagon is trying to juggle two competing missions in Africa: contain the spread of Islamist militancy without having to pour a lot of soldiers or money into the region.

Threats continue on the continent, but budgets are tightening at home and the appetite for sending large U.S. armies to foreign conflicts is small. So, the Obama administration is focusing on training and advising African troops to deal with their own security threats, or providing help to European allies who have historical ties and forces in the region.

U.S. officials and their partners call it enabling, a way of shifting from being a major combatant to offering support to local and other international forces. In the Central African Republic, U.S. transport planes recently ferried 1,700 peacekeepers from Burundi and Rwanda to the strife-torn nation, but put no U.S. boots on the ground. The United States is flying unarmed reconnaissance drones from a base in Niger to support French and African troops in Mali but conspicuously stayed out of the war there, even after the conflict helped spur a terrorist attack in Algeria in which Americans were taken hostage.

Across the continent this year, soldiers from a 3,500-member brigade in the Army’s storied 1st Infantry Division are conducting more than 100 missions, ranging from a two-man sniper team in Burundi to humanitarian exercises in South Africa.

As part of a three-week exercise, Army Green Berets from Fort Carson, Colo., and instructors from other Western countries have trained African troops in Niger to conduct combat patrols and to foil terrorist ambushes. But officials say they can also make headway in relatively simple, nonconfrontational ways, like the Pentagon’s help in organizing a medical clinic during the exercise for nearly 2,000 people in a nearby village, in the hope of encouraging intelligence sharing between the Niger military and the local population.

"If you can develop a trusting relationship with people, you can gather any information you need," Fougou Malam Saley, a U.S.-trained sergeant in Niger’s army, said before the medical event and a meeting with 15 community leaders from areas where Boko Haram uses subtle intimidation.

U.S. officials point out that they will intervene directly when vital interests are at stake. In South Sudan, U.S. soldiers and Marines positioned in the region after the attack on the U.S. mission in Benghazi, Libya, in 2012, rushed to help evacuate dozens of Americans from the embassy there last December. Commando raids last year in Libya (successful) and Somalia (failed) show the United States will not farm out its top counterterrorism missions, officials say.

But the weaknesses of the Pentagon’s strategy to outsource its security needs in stretches of Africa are also on display in Niger, where the government of President Mahamadou Issoufou is struggling to stem a flow of extremists across the country’s lightly defended borders with Mali, Nigeria and Libya. Even with Western aid, Niger’s top officials say, the challenge is daunting.

"Niger is suffering the collateral fallout of the Libyan and Malian crises," Niger Foreign Minister Mohamed Bazoum told a security conference in Niger last month.

In the past two years, the United States has spent $33 million to build Niger’s counterterrorism abilities, providing equipment such as radios, water and fuel trucks, spare parts, helmets, body armor, uniforms and GPS devices.

Here in this remote southeastern city, Niger’s security forces have stepped up patrols and created an intelligence unit to ferret out infiltrators.

Just across the border in Nigeria, there has been a recent surge of attacks by Boko Haram, which the State Department last November branded a terrorist group with links to al-Qaida in the Islamic Maghreb.

"A new generation of Boko Haram militants is displaying a greater appetite for violence," said a report issued last month by the U.N. office that monitors sanctions on al-Qaida and the Taliban.

U.S. officials are putting the finishing touches on a plan for U.S. Army instructors to help train 850 rangers as part of Nigeria’s new special forces command.

Some U.S. lawmakers say the administration’s level of involvement makes sense but argued that direct U.S. military engagement might have to increase if threats in the region rise.

"It’s a balancing act," said Rep. Frank A. LoBiondo, a New Jersey Republican on the Intelligence Committee who specializes in Africa and visited Niger and Nigeria in January. "Many of these countries consider the U.S. a partner and strong ally, but they have serious concerns about what our footprint looks like."

The U.S. strategy in Africa also hinges on European partners. In January, France began to reorganize its 3,000 troops in the Sahel region — a vast area on the southern flank of the Sahara that stretches from Senegal to Chad — to carry out counterterrorism operations more effectively, officials said. France will concentrate its air power in Chad, its new reconnaissance drones in Niger, its special operations troops in Burkina Faso and its logistics hub in Ivory Coast.

The United States has provided intelligence, as well as refueling and transport planes, to France, which intends to keep about 1,000 soldiers in Mali for counterterrorism missions.

"Leveraging and partnering with the French is a way to go," James R. Clapper Jr., the director of national intelligence, told Congress last month. "They have insight and understanding and, importantly, a willingness to use the forces they have there now."

Against this backdrop, the Pentagon’s Africa Command is running an annual exercise conducted since 2005 called Flintlock. This year, about 600 African troops and 500 Western trainers and support personnel, including about 300 Americans, participated here and in two cities in central Niger, Agadez and Tahoua.

In temperatures often above 100 degrees, African troops in groups of as many as 40 teamed up with advisers from the United States or European allies like Italy, France, Britain and Norway. They practiced marksmanship, patrolling harsh desert terrain and conducting vehicle checkpoints.

African militaries that just a few years ago barely cooperated are now testing new teamwork.

"We’re getting a lot of experience and, most important, we’re getting to know each other and operate together," said Capt. Oumar Enock, a ranking officer of three dozen soldiers from Chad.

The daily training has also revealed barriers that extremists could exploit.

Simple communications are often challenging. A Norwegian trainer’s explanation of patrolling tactics in English had to be translated into French and then again by another interpreter into Hausa, a language spoken by many of Niger’s troops. Any questions started the time-consuming linguistic chain in reverse.

In his office near the exercise, Col. Mounkaila Sofiani, the regional commander of Niger’s forces here, who has trained in Morocco and Senegal, and at Fort Benning, Ga., acknowledged the threat from Boko Haram but insisted his military did not need a permanent U.S. troop presence.

"If our troops are well-trained," he said, "we can handle these situations ourselves."