The Pentagon has secretly expanded its global network of drone bases­ to North Africa, deploying unmanned aircraft and U.S. military personnel to a facility in Tunisia to conduct spy missions in neighboring Libya.

The Air Force Reaper drones began flying out of the Tunisian base in late June and have played a key role in an extended U.S. air offensive against an Islamic State stronghold in neighboring Libya.

The Obama administration pressed for access to the Tunisian base as part of a security strategy for the broader Middle East that calls for placing drones and small Special Operations teams at a number of facilities within striking distance of militants who could pose a threat to the West.

U.S. officials, speaking on the condition of anonymity to discuss an operation that has not been acknowledged, said the drones being flown out of Tunisia were unarmed and were principally being used to collect intelligence on Islamic State targets in Sirte, Libya, where the United States has conducted more than 300 airstrikes since August.

U.S. officials said they sought access to the air base in Tunisia to close a critical “blind spot” for U.S. and Western intelligence services­ in North Africa, which has become the Islamic State’s largest base of operations outside of Syria and Iraq. The region is also home to al-Qaeda-linked fighters.

Obama administration officials say they have tried to shore up Tunisia’s fledgling democracy and position the country as a key counter­terrorism partner in the region. Although the drones operating out of Tunisia conduct only surveillance missions, U.S. officials said they could be armed in the future if Tunisia gives the United States permission. The Tunisian Embassy in Washington declined to comment.

The U.S. military has other drone bases­ on the African continent, from Niger to Djibouti. But officials said they were too far from populous areas on the Libyan coast to be useful in day-to-day counter­terrorism operations there. The longer drones have to travel to reach their destinations, the less time they have to “loiter” over their targets.

For lethal strikes in Libya, the U.S. military has relied on manned U.S. aircraft based in Europe and armed drones flown out of Naval Air Station Sigonella on the Italian island of Sicily.

Sigonella is relatively close to Sirte, but flights from the base are routinely canceled because of cloud cover over the Mediterranean and other weather-related issues, officials said.

U.S. logistical concerns about using Sigonella and other bases­ in Europe for operations in North Africa prompted the Pentagon’s push for a facility on Tunisian soil.

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The Obama administration has kept its negotiations over access to the base secret for more than a year because of concerns that Tunisia’s young democracy, worried about being closely associated with an outside military power, would pull out of the talks, or that militants would step up attacks in the North African country.

The Islamic State has already claimed a number of attacks in Tunisia over the past two years, including the killing of dozens of foreign tourists at a beach resort in 2015.

Defense officials said the Pentagon has deployed about 70 military personnel to Tunisia to oversee drone operations there.

Tunisia was the Obama administration’s first choice of countries in North Africa to host U.S. drones because of its proximity to Libya and Washington’s interest in rapidly expanding security ties with the government.

But U.S. officials said the negotiations came at a particularly delicate time. Five years after their uprising against dictator Zine el-Abidine Ben Ali, Tunisians have grown increasingly frustrated with many of their post-revolution leaders. In the summer, disaffection over the economy and security boiled over, leading to the premier’s ouster.

Tunisian officials negotiating the drone deal were particularly concerned about a public backlash over cooperation with a foreign power and wanted to avoid the appearance that they were a party to U.S. military operations in a neighboring country.

At the same time, Tunisian officials were eager to secure additional U.S. support for their counter­terrorism fight at home. Tunisian officials were especially worried that an eventual assault on Islamic State hideouts in Libya could send militants streaming across the border into Tunisia.

The United States was already conducting manned surveillance flights over Tunisia, providing the country’s security forces­ with intelligence about extremist threats. That program helped smooth the way in Tunis for Washington’s request to base drones there.

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U.S. military officials in Washington and Stuttgart, Germany, where Africa Command is based, grew increasingly eager to strike a deal with Tunisia this past spring. Opening a drone base there would help clear the way for the long-awaited Sirte operation, they said.

A brazen attack in March on a town near the Libyan border provided proof for some Tunisian officials of why more U.S. help might be required.

Under the memorandum of understanding giving the Pentagon access to the base, the Americans committed to helping build up Tunisia’s intelligence-collection capabilities.

While Tunisia is racing to grow its own aerial surveillance program, with U.S.-manufactured ScanEagles and other light manned surveillance aircraft, the country remains reliant on the United States and other allies for intelligence about militants.

As part of the new arrangements, the Obama administration agreed to share intelligence from the Reapers with Tunisian security forces­ to help them improve border security. But so far, the United States has made drone flights inside Libya the priority and officials said that is unlikely to change at least until the campaign in Sirte winds down. The battle in Sirte has already lasted far longer than U.S. officials had expected, as effective Islamic State de­fenses and repercussions from Libya’s political crisis slow the advance of local forces­ backed by U.S. air power.

The United States’ second military intervention in Libya in five years has underscored the challenge that the Obama administration has faced getting even close NATO allies such as Italy to open their bases­ to armed U.S. drones.

While U.S. surveillance drones have been based in Sigonella since 2011, the Italian government refused to give the U.S. military permission to fly armed drones out of the base until earlier this year, citing concerns about sparking an anti­war backlash at home.

Desperate to fill the intelligence void over Libya, the United States briefly had to use drones based in faraway Jordan.

The Obama administration had considered opening backup talks with Egypt about putting a drone base there to support operations in Libya. But U.S. officials said those talks were never initiated.

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