The CIA's internal watchdog is investigating allegations that the agency improperly spied on Senate staffers probing secret details of a now-defunct interrogation program.
Senator Dianne Feinstein acknowledged Wednesday the existence of the probe, which highlights a rare public clash between lawmakers on the Senate Intelligence Committee she chairs and the US espionage community it oversees.
"The IG is taking a look at the situation," Feinstein told reporters, referring to the Central Intelligence Agency's inspector general, after a New York Times report exposed Capitol Hill anger at CIA staffers' behavior.
According to the Times, the probe began when members of Congress complained that agency employees were inappropriately monitoring intelligence committee staffers.
The paper cited an official, who insisted on anonymity because the investigation was ongoing, as saying CIA officers managed to gain access to computer networks used by committee staffers probing the agency's detention and interrogation program.
The staffers had spent years researching and writing a 6,000-page bipartisan report that was highly critical of the program, which began under president George W. Bush.
In December 2012, when the report was approved by her committee, Feinstein described the creation of clandestine "black sites" and the use of enhanced interrogation techniques such as waterboarding as "terrible mistakes."
The McClatchy news service reported that the inspector general's office has asked the Justice Department to investigate the case.
But CIA Director John Brennan vehemently defended the spy agency and blasted some lawmakers for what he called unfounded allegations.
"I am deeply dismayed that some members of the Senate have decided to make spurious allegations about CIA actions that are wholly unsupported by the facts," Brennan said in a bluntly worded statement.
"I am very confident that the appropriate authorities reviewing this matter will determine where wrongdoing, if any, occurred in either the executive branch or legislative branch."
Feinstein and her committee have been in the spotlight in recent months for their strong support of National Security Agency espionage programs like those exposed by former contractor Edward Snowden.
Some lawmakers fumed that, if true, the alleged impropriety showed that the very separation of powers enshrined in the US Constitution was under threat.
"If they were doing that, I'm outraged," Senator John McCain told reporters, adding that a full investigation would be merited.
"You just can't have that happen in a democracy. There's a separation of powers between the legislative branch and the executive branch."
Senator Marco Rubio, a member of the panel, declined to comment on specific allegations.
But when asked whether the committee could provide adequate oversight of the CIA, he responded: "we endeavor to."
The controversy appeared to have been sparked by Senator Mark Udall, who the Times said wrote President Barack Obama on Tuesday to complain.
"As you are aware, the CIA has recently taken unprecedented action against the committee in relation to the internal CIA review, and I find these actions to be incredibly troubling for the committee's oversight responsibilities and for our democracy," Udall wrote, according to the Times.
But the CIA chief said senators should withhold public comment until the legal review is completed, warning they were jeopardizing the relationship between the intelligence agencies and Congress.
The American Civil Liberties Union rights group demanded a full accounting of any abuses.
"If it turns out that the CIA was spying on the Senate committee that oversees the agency, it would be an outrageous violation of separation of powers," said ACLU senior legislative counsel Christopher Anders.
"The CIA is prohibited from spying in the United States itself, and there can be few greater violations of that rule than spying on congressional staff carrying out the constitutional duty of being a check on the CIA's powers."