Row over claim CIA spied on US Senate

A rare public spat has erupted between the CIA and the US lawmakers meant to oversee its work, with the head of the agency angrily denying claims it spied on Senate staff.

Senate Intelligence Committee chairwoman Dianne Feinstein on Tuesday launched a fiery attack on the Central Intelligence Agency, accusing it of improperly searching computers used by staffers investigating CIA 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 violated federal law as well as the executive order that bars it from domestic spying, but the agency's director John Brennan denied the allegations.

"Nothing could be further from the truth," Brennan said at a Washington event.

Brennan also told NBC News: "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 the agency's controversial and now defunct interrogation program.

"I have asked for an apology and a recognition that this CIA search of computers ... was inappropriate," the Democratic senator from California said. "I have received neither."

At the White House, President Barack Obama's spokesman Jay Carney dodged all questions about the allegations.

"I can't comment on allegations that are under review," he said, adding that the White House took the concerns of Feinstein very seriously - but also saying 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.

The senator's comments came after unnamed administration officials alleged to news media that Senate staffers took sensitive documents without authority, triggering an investigation.

Feinstein has rejected those accounts.

The American Civil Liberties Union applauded Feinstein for her "necessary and historic defence of the constitutional principle of separation of powers".