The U.S. military believes one of its drones lost near Libya’s capital Tripoli on Nov. 21 was brought down by Russian air defenses, according U.S. Africa Command.

Air Force Col. Christopher Karns, a spokesman for AFRICOM , told Military Times that the U.S. believes the remotely piloted aircraft may have been brought down by Russian mercenaries or troops with Khalifa Hifter’s Libyan National Army operating a Russian air defense system.

The U.S. is working various diplomatic channels as it seeks return of the downed drone, Karns said.

The commander of AFRICOM, U.S. Army General Stephen Townsend told Reuters that he believes the individuals who shot down the drone “didn’t know it was a U.S. remotely piloted aircraft when they fired on it.”

Esper says US forces combating ISIS in Libya ‘continue to mow the lawn’ The 5-inch gun aboard the Arleigh Burke-class destroyer Carney lobbed nearly 285 rounds during the operation to wrest Sirte from ISIS’ grasp.

“But they certainly know who it belongs to now and they are refusing to return it. They say they don’t know where it is but I am not buying it,” Townsend told Reuters.

The U.S. has accused Russia of deploying mercenaries with the private security contractor the Wagner Group to Libya to support Hifter’s LNA forces.

Hifter’s forces are attempting to capture Tripoli from the UN-backed Government of National Accord.

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The Associated Press reported that the GNA has documented 600 to 800 Russian fighters in Libya, though Moscow denies it is involved in Libya’s civil war.

The collapse of Libyan dictator Moammar Gadhafi in 2011 plunged Libya into chaos and has pitted LNA forces under Hifter against the Tripoli-based GNA.

The U.S. uses drones in Libya to monitor the security situation and extremist groups like ISIS.

In September, U.S. airstrikes knocked out about one third of Islamic State’s fighters in Libya.

During a trip to South Korea in November Secretary of Defense Mark Esper was pressed about the U.S. airstrikes targeting Islamic State fighters in Libya and whether he was worried about an ISIS resurgence in the country.

"We continue — the phrase that people use is “continue to mow the lawn,” Esper responded. “And that means, every now and then, you have to do these things to stay on top of it so that a threat doesn’t grow, doesn’t resurge.”

Between Sept. 20 and Sept. 30, U.S. air assets conducted four airstrikes killing 43 ISIS fighters with about 100 still remaining, according to a senior U.S. defense official, who spoke with reporters on the condition of anonymity in October.

At its height of power in Libya in 2016, ISIS once controlled and dominated the city of Sirte. The jihadi fighters were expelled from the city by partner forces backed by American air power and naval gunfire during an operation dubbed Operation Odyssey Lightning.

Karns told Military Times that the U.S. believes that the forces that shot down the U.S. drone over Libya may have mistaken it for an opposition drone.

Reuters first broke the news that Russian air defenses may have been responsible for the downing of a U.S. drone near Tripoli in November.