The US attorney general has refused to tell Congress about a government probe into why the CIA destroyed recordings of interrogations of terror suspects.
The Democratic-led House failed to block "enhanced interrogation"
Michael Mukasey said giving details might suggest that political pressure could sway law enforcement decisions.
The tapes were said to show techniques such as water-boarding, which simulates drowning. The CIA denies torture.
Meanwhile, Republican Senators have blocked a bill restricting the interrogation methods the CIA can use.
The House of Representatives passed the bill on Thursday before passing it to the Senate.
Among its provisions the bill would restrict the use of water-boarding, regarded as a form of torture by many human rights advocates.
In letters to the House and Senate committees investigating the destruction of the interrogation tapes, Mr Mukasey said he saw no need to appoint a special prosecutor into the issue.
"I am aware of no facts at present to suggest that department attorneys cannot conduct this inquiry in an impartial manner," he wrote.
"If I become aware of information that leads me to a different conclusion, I will act on it."
His decision was criticised by Republicans and Democrats, who said Mr Mukasey was hampering congressional oversight of the justice department.
"We are stunned that the justice department would move to block our investigation," the joint leaders of the House Intelligence Committee said in response.
Earlier in the week CIA director Michael Hayden told the committee that he had no prior knowledge of plans to destroy the tapes and that his organisation "could have done an awful lot better" in keeping Congress informed on the issue.
He said last week that the tapes of the interrogations of two alleged al-Qaeda operatives had been destroyed because they were no longer of intelligence value and to protect the identities of agents.
The destruction of the recordings has provoked concern among some lawmakers and human rights groups.
"It smells like the cover-up of the cover-up," said Democratic Rep Jane Harman, who chairs the House Homeland Security subcommitee on intelligence.
"The destruction of these tapes appears to be a part of an extensive, long-term pattern of misusing executive authority to insulate individuals from criminal prosecution for torture and abuse," the American Civil Liberties Union said in a statement said.