NIAMEY, Niger » Nearly every day, and sometimes twice daily, an unarmed U.S. drone soars skyward from a secluded military airfield here, starting a surveillance mission of 10 hours or more to track fighters affiliated with al-Qaida and other militants in neighboring Mali.

The two MQ-9 Reapers that are based here stream live video and data from other sensors to U.S. analysts working with French commanders, who say the aerial intelligence has been critical to their success over the past four months in driving jihadists from a vast desert refuge in northern Mali.

The drone base, established in February and staffed by about 120 members of the Air Force, is the latest indication of the priority Africa has become for the U.S. at a time when it is winding down its presence in Afghanistan and President Barack Obama has set a goal of moving from a global war on terrorism toward a more targeted effort. It is part of a new model for counterterrorism, a strategy designed to help local forces — and in this case a European ally — fight militants so U.S. troops do not have to.

But the approach has limitations on a continent as large as Africa, where a shortage of resources is chronic and regional partners are weak. And the introduction of drones, even unarmed ones, runs the risk of creating the kind of backlash that has undermined U.S. efforts in Pakistan and provoked anger in many parts of the world.

The increase in the number of potential threats in the region was made clear to Obama during his visit to Africa last week.

"We need in Africa, not just in Senegal but the whole of Africa, to have the military capacity to solve this problem, but we need training, we need materials, we need intelligence," President Macky Sall of Senegal told Reuters after meeting with Obama in Dakar to discuss fears of a growing violent Islamist threat in the Sahara.

The U.S. military, however, has only one permanent base in Africa, in Djibouti, more than 3,000 miles from Mali, as well as a constellation of small airstrips, including in Ethiopia and Burkina Faso, for surveillance missions flown by drones or turboprop planes designed to look like civilian aircraft. The challenge for the U.S., with little experience in Africa, is a difficult one.

"The U.S. is facing a security environment in Africa that is increasingly more complex and therefore more dangerous," said Michael R. Shurkin, a former Central Intelligence Agency analyst who is now at the RAND Corp. "Effective responses, moreover, require excellent knowledge about local populations and their politics, the sort of understanding that too often eludes the U.S. government and military."

And the threats facing Niger are typical of the ones that worry Sall. The government of President Mahamadou Issoufou is struggling to stem a flow of insurgents across lightly guarded borders with Mali, Nigeria and Libya. On May 23, terrorists using suicide car bombs attacked a Nigerien military compound in Agadez and a French-operated uranium company in Arlit, both in the country’s north.

Two groups claimed credit for the bombings, which the authorities in Niger say killed at least 24 soldiers and one civilian, as well as 11 militants: one led by the Algerian militant Mokhtar Belmokhtar, which carried out an attack on a large gas field in Algeria in January, as well as a regional offshoot of al-Qaida, the Movement for Oneness and Jihad in West Africa, or Mujao.

The terrorist attacks in May, combined with an escape from Niamey’s biggest jail last month by 32 detainees, including many suspected militants, have left Issoufou’s government vulnerable to criticism that it cannot provide security, despite allowing U.S. drones on Nigerien soil.

The government in Niger has defended that decision, and it is concerned enough about the threat it perceives from extremist fighters pushed out of Mali that it initially wanted the drones to be armed, a former senior U.S. official said. But Obama administration officials thought that was unnecessary and politically unwise.

To experts on Africa, the possibility that the drones will yet cause a backlash remains real, especially if Islamic radicals make it an issue.

"The concern would be that a lot of the blowback would be through channels we can’t easily perceive, such as Salafist mosques," said Alexis Arieff, an Africa analyst with the Congressional Research Service in Washington.

The U.S. acknowledged the drone deployment here in February — initially sending a single Predator aircraft and later faters, more capable Reapers — but since then it has released virtually no information about their missions, presumably to avoid raising their public profile. The Pentagon denied a request by The to interview the Air Force flight crews, logistics and maintenance specialists, and security personnel assigned here at a military airfield on the opposite side of the commercial airport in Niger’s capital.

French, U.S. and Nigerian officials all have a say in the daily missions of the drones, a Pentagon official said, but clearly the priority has been supporting the French campaign in Mali. The U.S. has flown more than 200 missions in support of the French campaign, with the possibility that it could expand its operations to support a U.N. force largely composed of African troops that assumed control of the peacekeeping mission in Mali on July 1.

In some of the fiercest fighting between French-led forces and the Islamist fighters in early March, the drones hovered over a rugged mountainous region in Mali, giving allied forces targeting information for airstrikes. French and African officials say that perhaps 700 fighters, out of about 2,000 insurgents in all, were killed in the fighting.

As surviving fighters have melted back into the desert and mountains in recent weeks, the Reapers have been surveilling vast reaches of the north for signs of militant infiltration or secret new redoubts — a daunting task that one U.S. official described as "looking through a soda straw" across the Sahara. At Niger’s request, U.S. officials said, the drones may also conduct surveillance along the border before entering Mali.

Despite the gains, J. Peter Pham, the director of the Atlantic Council’s Africa Center in Washington, said the French were not fully using the information from the drones. The French forces, fearing attack from surface-to-air missiles looted from Libyan stockpiles, have curtailed helicopter gunship missions in Mali, and they instead rely on higher-flying but less precise fighter-bombers for any airstrikes, Pham said. But a French official said France had not carried out airstrikes in weeks and played down the missile threat. The official said that the intelligence was still being used to support ground operations.

The U.S. missions have not been without incident. On April 9, one of the drones crashed in a remote part of northern Mali, presumably because of a mechanical failure. "It was a total loss," one Air Force officer said of the wreckage.

Pentagon officials say the drone missions will continue even as France reduces its force in Mali to about 1,000 troops by year’s end, from 3,500 now, "because we see a continued need for intelligence collection in that region," said Amanda Dory, deputy assistant secretary of defense for Africa.

France has been impressed enough with the Reapers that it intends to buy at least two of the aircraft from the U.S. "They’ve been absolutely necessary for us because we don’t have enough drones to protect our troops and to get permanent visibility about what’s happening on the ground," said a French defense official in Paris.

© 2013 The New York Times Company