"The CIA no longer operates detention facilities or black sites and has proposed a plan to decommission the remaining sites," CIA Director Leon Panetta said in a letter to staff that was released on the CIA's website.

"I have directed our agency personnel to take charge of the decommissioning process and have further directed that the contracts for site security be promptly terminated," he said.

Panetta said the CIA still reserved the right to hold suspects for a brief period before handing them over to military authorities.

The CIA statement is said to confirm that the spy service was carrying out an order from President Barack Obama to shut down the secret detention centres.