The U.S. military believes the unarmed drone that went missing over the Libyan capital last month was actually shot down by Russian air defenses.

The U.S. Africa Command is demanding the return of the aircraft's wreckage, which had been part of an operation conducted in Libya to assess the area's security and monitor for violent extremist activity. The command didn't give a reason for the drone loss after the Nov. 21 incident, but they had been investigating, Reuters reported.

Army General Stephen Townsend told the outlet he believed Russia's air defense operators at the time "didn't know it was a U.S. remotely piloted aircraft when they fired on it."

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

The U.S. assessment concluded that either Russian private military contractors or the National Army of east Libya-based commander Khalifa Haftar's were operating the defenses when the drone was lost, according to Africa Command spokesman, Air Force Colonel Christopher Karns. Forces loyal to the eastern government have been trying to wrest control of the capital since April.

An official in Libya's Government of National Accord (GNA) told Reuters that Russian mercenaries appeared to be responsible. Karns added that the unnamed aircraft was fired upon by air defense operators after "mistaking it for an enemy" drone.

The attack emphasizes Moscow's role in the energy-rich country, according to the outlet. Russian mercenaries have been reportedly intervening on behalf of Hafter during a civil war for the energy-rich country, Reuters reported.

A former and current Russian contractor told Reuters that the Libyan National Army (LNA) had received aid from hundreds of private military contractors from a Russian group.

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However, Russian authorities have denied using military contractors in any foreign operation. They claim any civilians who may be fighting abroad are volunteers. The Libyan National Army has also denied receiving foreign backing.

General Townsend has also voiced his concerns about Russia's role impacting AFRICOM's counter-terrorism mission in Libya.

“This highlights the malign influence of Russian mercenaries acting to influence the outcome of the civil war in Libya, and who are directly responsible for the recent and sharp increase in fighting, casualties, and destruction around Tripoli,” Townsend told the outlet.

In September, the U.S. military said it carried out several airstrikes against the Islamic State group in Libya, killing more than 40 militants. Those were the first U.S. strikes in the North African country in over a year.

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Oil-rich Libya descended into chaos in 2011 when an international military coalition helped rebels overthrow longtime autocrat Moammar Gadhafi. Islamic extremists have exploited the chaos to expand their reach in the country.

The Associated Press contributed to the report