WASHINGTON (AFP) - A top US lawmaker's hotly disputed charge that the CIA illegally spied on Senate staff has roiled the intelligence community, fraying ties between the agency and its overseers in Congress.
Senator Dianne Feinstein brought what had been a behind-the-scenes spat into the public glare on Tuesday with her furious broadside against the Central Intelligence Agency, saying its agents searched computers used by staffers investigating its interrogation methods.
"I have grave concerns that the CIA's search may well have violated the separation of powers principles embodied in the United States Constitution," Feinstein said on the Senate floor.
She alleged the CIA may have breached federal law as well as the executive order that bars it from domestic spying, but the agency's director John Brennan quickly denied the allegations.
"Nothing could be further from the truth," Brennan said at a Washington event.
"The matter is being dealt with in an appropriate way, being looked at by the right authorities, and the facts will come out."
Feinstein said the CIA searched a computer drive used by staffers on the intelligence committee to prepare a major report into a controversial and now defunct agency interrogation program that used "enhanced interrogation techniques" against detainees.
"I have asked for an apology and a recognition that this CIA search of computers... was inappropriate," the California Democrat said. "I have received neither."
The reverberations shuddered across Washington, as lawmakers voiced concern about a steady infringement on their duty to keep the CIA and National Security Agency in check.
"Today the debate goes right to the heart of the question of how Congress can do effective oversight (of) the modern intelligence apparatus," Senator Ron Wyden, an intelligence committee panel who has long argued that the spy agencies abuse their authority, told reporters.
Senator Lindsey Graham went as far as to declare the actions reminiscent of president Richard Nixon's misdeeds.
"Heads should roll, people should go to jail if it's true," Graham told reporters.
"If it is, the legislative branch should declare war on the CIA."
Feinstein herself described the CIA interference as a defining moment.
"How this will be resolved will show whether the intelligence committee can be effective in monitoring and investigating our nation's intelligence activities, or whether our work can be thwarted by those we oversee."
President Barack Obama's spokesman Jay Carney dodged repeated questions about the row, saying the case had been referred to the Justice Department.
"I can't comment on allegations that are under review," he said, adding that the White House took the concerns of Feinstein seriously - but also saying that Obama had full confidence in Brennan.
Feinstein's extraordinary speech marked a break from her usually cordial relations with the intelligence community, which she has often defended against accusations of overstepping its authority.
Her comments came after unnamed administration officials alleged to news media that Senate staffers took sensitive documents without authority, triggering an investigation.
Feinstein rejected those accounts.
She said the CIA and the committee had agreed years ago to set up a secure site in Virginia for Senate staff to review documents, as well as a computer drive separate from the agency's network.
The staffers reviewed 6.2 million documents and at no point did they seek to retrieve files that were marked classified or legally off-limits, she said.
Feinstein said 870 documents were removed by the CIA in February 2010, while 50 others were withdrawn without committee knowledge.
The interrogation report was completed in December 2012, when the committee approved a 6,300-page study that has yet to be released publicly.
Feinstein said a CIA internal review of the interrogation program was among the documents provided to her staff, but that CIA officials demanded to know how staffers obtained the review.
Analysts say the Congress-CIA rift is the worst since the 1970s, when lawmakers uncovered illegal abuses and introduced legal reforms to restrict the power of the spy services.
But the intelligence community today faces rising public anger over shock revelations that the NSA scoops up telephone data from most Americans.
Fugitive former security contractor Edward Snowden told NBC News that "the CIA was trying to play 'keep away' with documents relevant to an investigation by their overseers in Congress." "That's a serious constitutional concern," he said.