The US military reported Sunday that a once-secret unit inside the Guantanamo Bay detention center has been closed and the inmates relocated to another facility on the American base in Cuba.

In an attempt to “increase operational efficiency and effectiveness,” the prisoners at Camp 7 were moved to a facility adjacent to where the other inmates on the base are housed, according to a statement from US Southern Command.

The detention center on Cuba's southeastern border is overseen by the United States' Southern Command, which is headquartered in Miami. Officials previously reported that approximately 14 men were held in Camp 7. At Guantanamo, there are 40 captives.

The prisoners from Camp 7 were transferred to Camp 5 "safely and without incident," according to Southern Command, but it did not indicate when the transfer took place. Camp 5, which was mostly vacant, is adjacent to Camp 6, which houses the remaining detainees.

In December 2006, Camp 7 opened for prisoners who had previously been imprisoned in a network of covert CIA detention centers known as "black sites," where they were subjected to extreme interrogation techniques. It was run by the military under an arrangement with the CIA, and the transition was overseen by intelligence agencies, according to Southern Command.

The military has long declined to recognize Camp 7's existence on the base and has never allowed journalists to visit the site. Officials said the unit, which was never intended to be permanent, had structural problems and needed to be replaced, but the Pentagon decided not to pursue funding for the project.

The five prisoners charged with war crimes for their suspected roles in preparing and providing logistical support for Sept. 11, 2001, terrorist attacks were among those held at Camp 7.

President Joe Biden has stated his desire to close Guantánamo, although this would necessitate congressional permission to transfer any detainees to the United States for trial or incarceration.