"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.

Human-rights groups have condemned the treatment of al-Qaeda terrorist suspects in secret CIA prisons in foreign countries. Rights groups and media reports have alleged the secret prisons were located in Central and Eastern Europe, including Poland, Romania and in former Yugoslavia, as well as in the Horn of Africa and on US Navy ships.

Obama pledges to reverse Bush's policies

Obama has already ordered the eventual closure of the controversial prison camp in Guantanamo Bay, Cuba, and repealed some of the harsh interrogation tactics used under President George W Bush while repeating his mantra that the United States "does not torture."

In 2006, Bush first acknowledged the existence of the secret prisons, which were used to hold high-profile suspects including Khalid Sheikh Mohammed, the alleged mastermind of the attacks on Sept. 11, 2001.

The prisons' existence caused problems for some governments in Europe and Asia who allegedly were aware of the facilities. A European Union report in 2007 singled out Poland and Romania for allowing CIA prisons on their soil from between 2002 and 2005, although both denied any knowledge.

Red Cross accuses CIA of torture

The harsh methods employed under the Bush administration, including simulated drowning or "waterboarding" of detainees, were widely condemned as torture and abuse. An internal report leaked last month from the International Committee of the Red Cross said the CIA's interrogations amounted to torture.

The report concluded that the treatment of inmates at black sites run by the CIA amounted to "cruel, inhuman or degrading treatment," prohibited by the Geneva Conventions.

The conclusions by ICRC officials came after they were granted exclusive access to the CIA's "high-value" detainees who had been transferred in 2006 to the Guantanamo Bay prison.