WASHINGTON (Reuters) - U.S. civil rights groups on Monday called on the U.S. Justice Department to appoint a special prosecutor to investigate the CIA's use of torture and other extreme measures during interrogations.

The American Civil Liberties Union and Human Rights Watch said in a letter to Attorney General Eric Holder that the recent Senate Intelligence Committee report on the CIA included significant new information about the nature of tactics, the decisions that led to their use and the number of prisoners involved.

Administration officials have said the Justice Department has no plans to reopen its investigation into the conduct of CIA interrogators toward detainees captured after the Sept. 11, 2001, attacks on the United States.

But the groups said the report's findings warranted a fresh criminal investigation.

"We believe the failure to conduct a comprehensive criminal investigation would contribute to the notion that torture remains a permissible policy option for future administrations; undermine the ability of the United States to advocate for human rights abroad; and compromise Americans' faith in the rule of law at home," the groups wrote.

Justice Department spokesman Marc Raimondi said authorities had already conducted two criminal investigations but that the Department had declined to prosecute anyone on the grounds of insufficient admissible evidence.

He said investigators had reviewed the Senate committee's report but found no "new information" that they had "not previously considered."

International human rights monitors and politicians, including United Nations figures, have also called for criminal investigations of U.S. officials implicated in the CIA's harsh interrogations.

(Reporting by Alina Selyukh and Mark Hosenball; Editing by Karey Van Hall and Richard Chang)