The CIA's internal watchdog is investigating allegations that the agency improperly spied on US Senate staffers probing secret details of a now-defunct interrogation programme.
Senator Dianne Feinstein acknowledged on 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 said, referring to the Central Intelligence Agency's inspector general, after a report in The New York Times exposed Capitol Hill anger at CIA staffers' behaviour.
According to the Times report, the probe began when members of Congress complained that agency employees were inappropriately monitoring intelligence committee staffers.
The newspaper 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 programme.
The staffers had spent years researching and writing a 6,000-page bipartisan report that was highly critical of the programme, which began under former 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".
Lawmakers were furious 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 said, adding that a full investigation would be merited.
He said: "You just can't have that happen in a democracy. There's a separation of powers between the legislative branch and the executive branch."