David Passaro, a CIA contractor, was convicted and sentenced to eight years for beating an Afghan detainee in 2007. The detainee later died.

'Investigations undermined'

"If criminal investigations closed by career prosecutors during one administration can so easily be reopened at the direction of political appointees in the next, declinations of prosecution will be rendered meaningless," the former CIA directors said in their letter to the White House.

"As a result of the zeal on the part of some to uncover every action taken in the post-9/11 period, many countries may decide that they can no longer safely share intelligence or cooperate with us on future counter-terrorist operations"

Excerpty from the letter, signed by former CIA directors, to the White House

The White House did not immediately respond to a request for comment.

The seven former directors include Michael Hayden, Porter Goss and George Tenet, who served under Bush.

John Deutch and James Woolsey, who worked for Bill Clinton; William Webster, who served under George HW Bush; and James Schlesinger, who ran the agency under Richard Nixon, are also signatories to the letter.

The ex-directors said that Obama should cancel Holder's decision to reopen the investigation of interrogations conducted by CIA staff after the attacks on September 11, 2001.

Paul Gimigliano, a spokesman for the CIA, said that it the agency is co-operating with the justice department review but that it will defend its agents.

"The (CIA) director has stood up for those who followed legal guidance on interrogation, and he will continue to do so," Gimigliano said.

Panetta opposed

The former directors said that criminal investigations against CIA staff could discourage officers from conducing aggressive intelligence work that they argue is needed to counter terrorism.

Foreign governments may also be less likely to grant intelligence findings to the CIA in future if the investigations go ahead, they said.

"As a result of the zeal on the part of some to uncover every action taken in the post-9/11 period, many countries may decide that they can no longer safely share intelligence or cooperate with us on future counter-terrorist operations," the letter said.

"They simply cannot rely on our promises of secrecy."
 
Leon Panetta, the current CIA director, also opposes Holder’s order for an investigation, although he did not sign the letter to Obama.

"I think the reason I felt the way I did is because I don't believe there's a basis there for any kind of additional action," Panetta said earlier this week.

"My concern is ... that we don't get trapped by the past. My feeling is ultimately, we're going to be able to move on."