The head of the U.S. Senate Intelligence Committee accused the CIA Tuesday of criminal activity in improperly searching a computer network set up for lawmakers investigating allegations that the agency used torture in terror investigations during the Bush administration.

California democrat Dianne Feinstein, in an extraordinary speech on the Senate floor, publicly aired an intense but formerly quiet dispute between Congress and the spy agency. She said the matter has been referred to the Justice Department for further investigation.

Both Feinstein and the CIA have accused each other's staffs of improper behaviour. She said she had "grave concerns that the CIA's search may well have violated the separation of powers principles embodied in the U.S. Constitution."

CIA Director John Brennan, asked about Feinstein's accusations, said the agency was not trying to stop the committee's report and that it had not hacked into Senate computers. He said the appropriate authorities would look at the matter further and "I defer to them to determine whether or not there was any violation of law or principle."

The CIA provided computers to congressional staffers in a secure room in northern Virginia in 2009 so the panel could review millions of pages of top secret documents in the course of its investigation into the CIA's detentions and interrogations during the Bush administration.

At issue now is whether the CIA violated an agreement made with the Senate Intelligence Committee about monitoring the panel's use of CIA computers.

'If we do not stand up for the protection of the separation of powers and our ability to do oversight, especially when conduct has happened that is all likelihood criminal conduct on the part of a government agency, then what do we stand for?'- Democratic Senator Patrick Leahy, chairman of the Senate Judiciary Committee

Feinstein said the Senate staff members had an electronic search tool to deal with 6.2 million pages of documents and the ability to make copies on their computers. She said the arrangement suffered a blow when CIA personnel electronically removed the committee's access to documents that had already been provided to the panel.

She said about 870 documents were removed in February 2010, and an additional 50 were withdrawn without the knowledge of the committee.

Feinstein said she has asked the agency for an apology but the CIA has been silent. CIA Director John Brennan, who first told Feinstein about the surveillance of the Senate investigation that occurred before he took over the CIA, had no immediate comment on the senator's statement.

The dispute comes as the Obama administration is trying to regain public trust after classified details about widespread surveillance of Americans were disclosed by former National Security Agency systems analyst Edward Snowden last summer.

Spy agencies vs. Congress

This dispute does not involve the NSA spying on Americans, but it does show a fractious relationship between the U.S. spy agencies and the Congress charged with overseeing them.

Feinstein, as head of the Intelligence panel, has defended the NSA against criticism of its practices, making her comments about the CIA dispute highly unusual. Senators said the stakes demanded it.

"If we do not stand up for the protection of the separation of powers and our ability to do oversight, especially when conduct has happened that is all likelihood criminal conduct on the part of a government agency, then what do we stand for?" asked Senator Patrick Leahy, chairman of the Judiciary Committee.

CIA Investigation

California Senator Dianne Feinstein, a member of the Senate Intelligence Committee, caused a fire storm of controversy in Washington, D.C. on Tuesday morning after accusing the CIA of accessing a closed computer network intended to be used only by Congress to investigate the Bush-era detention program. (Senate Television/Associated Press)

Saying she wanted to set the record straight amid various published reports and rampant speculation, Feinstein said the CIA searched the computer network in January and she had pressed Brennan about the agency's actions and the legal basis for its search.

She said she had not received any answers despite letters sent on Jan. 17 and Jan. 23.

Feinstein said the CIA's inspector general, David Buckley, has referred the matter to the Justice Department "given the possibility of a criminal violation by CIA personnel."

Escalating tensions

In further evidence of the escalating fight, Feinstein said that after the inspector general's referral, the acting counsel of the CIA filed a criminal report with the Justice Department regarding the committee staff's actions.

Feinstein defended the staff as professionals with appropriate security clearances.

"I view the acting counsel general's referral as a potential effort to intimidate this staff, and I am not taking it lightly," she said.

Brennan, who was questioned at an appearance on another subject, said "We are not in any way, shape or form trying to thwart this report."

"I am confident that the authorities will deal with this appropriately," he said. "I would just encourage some members of the Senate to take their time, to make sure they don't overstate what they claim and what they apparently believe to be the truth."

Democrats on the Senate Intelligence Committee completed their 6,300-page interrogation report last year and are revising it with CIA comments. Feinstein said she would ask the White House to declassify its 300-plus-page executive summary, and its conclusions.

When the report was first approved by Democrats on the committee in December 2012, Feinstein said her staffers came to the conclusion that the detention and interrogation program yielded little or no significant intelligence.

Presidential support

During a news briefing on Tuesday, White House spokesperson Jay Carney said that President Obama "has great confidence in John Brennan and confidence in our intelligence community and in our professionals at the CIA."

"We take everything [Feinstein] says very seriously and we take this seriously. But I'm not going to comment on matter that are under investigation or reviewed by the appropriate authorities," Carney added. 

Carney went on to say that the White House has been in communication with both the Senate Intelligence Committee chairman and Brennan.