By Phil Helsel and Associated Press

The U.S. military said late Friday that an unmanned drone was lost over the Libyan capital this week.

The "remotely piloted aircraft" was lost over Tripoli on Thursday, U.S. Africa Command said in a brief statement. The drone was not armed.

The military said the incident remains under investigation, but noted that the drones are critical to counter-terror efforts in the country.

The U.S. operations "are conducted in Libya to assess the ongoing security situation and monitor violent extremist activity," the statement said.

The type of drone and more details about the aircraft lost were not disclosed.

Rival groups have been fighting for control of Tripoli for months.

Since 2015, Libya has been divided between two governments, one based in Tripoli and the other in the country’s east.

Forces loyal to the eastern government have been trying to wrest control of the capital since April.

The North African nation has been divided and chaotic on becoming a failed state ever since NATO intervention, including American airstrikes, helped topple dictator Moammar Gadhafi in 2011.

Islamic extremists have been said to have taken advantage of the unstable situation.

In September U.S. Africa Command carried out four airstrikes in the country, targeting what it said were "ISIS-Libya terrorists" — a name by which the Islamic State terror group is also known.

The most recent strike was in southern Libya on Sept. 29, when it said 7 were killed.