DIRKOU, Niger (NYTIMES) - The CIA is poised to conduct secret drone strikes against Al-Qaeda and Islamic State in Iraq and Syria (ISIS) insurgents from a newly expanded air base deep in the Sahara, making aggressive use of powers that were scaled back during the Obama administration and restored by President Donald Trump.

Late in his presidency, Barack Obama sought to put the military in charge of drone attacks after a backlash arose over a series of highly visible strikes, some of which killed civilians. The move was intended, in part, to bring greater transparency to attacks that the United States often refused to acknowledge its role in.

But now the CIA is broadening its drone operations, moving aircraft to northeastern Niger to hunt Islamist militants in southern Libya. The expansion adds to the agency's limited covert missions in eastern Afghanistan for strikes in Pakistan, and in southern Saudi Arabia for attacks in Yemen.

Nigerien and US officials said the CIA had been flying drones on surveillance missions for several months from a corner of a small commercial airport in Dirkou. Satellite imagery shows that the airport has grown significantly since February to include a new taxiway, walls and security posts.

One US official said the drones had not yet been used in lethal missions, but would almost certainly be in the near future, given the growing threat in southern Libya. The official spoke on the condition of anonymity to discuss the secretive operations.

A CIA spokesman, Tim Barrett, declined to comment. A Defence Department spokeswoman, Major Sheryll Klinkel, said the military had maintained a base at the Dirkou airfield for several months but did not fly drone missions from there.

The drones take off from Dirkou at night - typically between 10 pm and 4 am - buzzing in the clear, starlit desert sky.

A New York Times reporter saw the gray aircraft - about the size of Predator drones, which are 27 feet long - flying at least three times over six days in early August. Unlike small passenger planes that land occasionally at the airport, the drones have no blinking lights signalling their presence.

"All I know is they're American," Niger's interior minister, Mohamed Bazoum, said in an interview. He offered few other details about the drones.

Dirkou's mayor, Boubakar Jerome, said the drones had helped improve the town's security.

"It's always good. If people see things like that, they'll be scared," Jerome said.

Obama had curtailed the CIA's lethal role by limiting its drone flights, notably in Yemen. Some strikes in Pakistan and elsewhere that accidentally killed civilians, stirring outrage among foreign diplomats and military officials, were shielded because of the CIA's secrecy.

As part of the shift, the Pentagon was given the unambiguous lead for such operations. The move sought, in part, to end an often awkward charade in which the United States would not concede its responsibility for strikes that were abundantly covered by news organisations and tallied by watchdog groups.

However, the CIA programme was not fully shut down worldwide, as the agency and its supporters in Congress balked.

The drone policy was changed last year, after Mike Pompeo, the CIA director at the time, made a forceful case to Trump that the agency's broader counterterrorism efforts were being needlessly constrained. The Dirkou base was already up and running by the time Pompeo stepped down as head of the CIA in April to become Trump's secretary of state.

The Pentagon's Africa Command has carried out five drone strikes against Al-Qaeda and ISIS militants in Libya this year, including one two weeks ago.

The military launches its MQ-9 Reaper drones from bases in Sicily and in Niamey, Niger's capital, 800 miles southwest of Dirkou.

But the CIA base is hundreds of miles closer to southwestern Libya, a notorious haven for Al-Qaeda and other extremist groups that also operate in the Sahel region of Niger, Chad, Mali and Algeria. It is also closer to southern Libya than a new US$110 million drone base in Agadez, Niger, 350 miles west of Dirkou, where the Pentagon plans to operate armed Reaper drone missions by early next year.

Another US official said the CIA began setting up the base in January to improve surveillance of the region, partly in response to an ambush last fall in another part of Niger that killed four US troops.

The Dirkou airfield was labelled a US Air Force base as a cover, said the official, who spoke on the condition of anonymity to discuss confidential operational matters.

The CIA operation in Dirkou is burdened by few, if any, of the political sensitivities that the US military confronts at its locations, said one former US official involved with the project.

Even so, security analysts said, it is not clear why the US needs both military and CIA drone operations in the same general vicinity to combat insurgents in Libya. France also flies Reaper drones from Niamey, but only on unarmed reconnaissance missions.

"I would be surprised that the CIA would open its own base," said Bill Roggio, editor of the Foundation for Defence of Democracies' Long War Journal, which tracks military strikes against militant groups.

Despite US denials, a Nigerien security official said he had concluded that the CIA launched an armed drone from the Dirkou base to strike a target in Ubari, in southern Libya, on July 25. The Nigerien security official spoke on the condition of anonymity to discuss the classified programme.

A spokesman for the Africa Command, Major Karl Wiest, said the military did not carry out the Ubari strike.

Ubari is in the same region where the US military in March launched its first-ever drone attack against Al-Qaeda militants in southern Libya. It is at the intersection of the powerful criminal and extremist currents that have washed across Libya in recent years.

Roughly equidistant from Libya's borders with Niger, Chad and Algeria, the area's seminomadic residents are heavily involved in the smuggling of weapons, drugs and migrants through the lawless deserts of southern Libya.

Some of the residents have allied with Islamist militias, including Al-Qaeda in the Islamic Maghreb, which operates across Algeria, Mali, Niger and Libya.

Dirkou, in northeast Niger, is an oasis town of a few thousand people in the open desert, bordered by a small mountain range. For centuries, it has been a key transit point for travellers crossing the Sahara. It helped facilitate the rise of Islam in West Africa in the 9th century, and welcomed salt caravans from the neighbouring town of Bilma.

The town has a handful of narrow, sandy roads. Small trees dot the horizon. Date and neem trees line the streets, providing shelter for people escaping the oppressive midday heat. There is a small market, where goods for sale include spaghetti imported from Libya. Gasoline is also imported from Libya and is cheaper than elsewhere in the country.

The drones based in Dirkou are loud, and their humming and buzzing drowns out the bleats of goats and crows of roosters.

"It stops me from sleeping," said Ajimi Koddo, 45, a former migrant smuggler.

"They need to go. They go in our village, and it annoys us too much." Satellite imagery shows that construction started in February on a new compound at the Dirkou airstrip. Since then, the facility has been extended to include a larger paved taxiway and a clamshell tent connected to the airstrip - all features that are consistent with the deployment of small aircraft, possibly drones.

Five defensive positions were set up around the airport, and there appear to be new security gates and checkpoints both to the compound and the broader airport.

It is not the first time that Washington has eyed with interest Dirkou's tiny base. In the late 1980s, the United States spent US$3.2 million renovating the airstrip in an effort to bolster Niger's government against Moammar Gadhafi, then the leader of Libya.

Compared with other parts of Africa, the CIA's presence in the continent's northwest is relatively light, according to a former State Department official who served in the region. In this part of Niger, the CIA is also providing training and sharing intelligence, according to a Nigerien military intelligence document reviewed by The Times.

The Nigerien security official said about a dozen US Green Berets were stationed earlier this year in Dirkou - in a base separate from the CIA's - to train a special counterterrorism battalion of local forces. Those trainers left about three months ago, the official said.

It is unlikely that they will return anytime soon. The Pentagon is considering withdrawing nearly all US commandos from Niger in the wake of the deadly October ambush that killed four US soldiers.