According to a report in McClatchy, the CIA secretly monitored computers used by Senate Intelligence Committee staffers that the spy agency had provided for the review of thousands of pages of classified documents.

The alleged monitoring occurred as the Senate Intelligence Committee prepared a 6,000 page report into the CIA's post-9/11 torture program, details from which the agency has fought to keep secret. The CIA responded to the investigation, which McClatchy described as a "searing indictment" of the program, with an "unprecedented action," as Senator Mark Udall put it in a letter to President Obama. The CIA's inspector general has launched an investigation into the matter.

"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. "It is essential that the Committee be able to do its oversight work — consistent with our constitutional principle of the separation of powers — without the CIA posing impediments or obstacles as it is today."

The specifics of the "unprecedented action" weren't released or discussed in the letter, but officials told McClatchy and the New York Times that the CIA monitored the computers used by Intelligence Committee aides in a secure room at the agency's headquarters in Langley, Va.

The New York Times reports the alleged spying took place "after C.I.A. officials came to suspect that congressional staff members had gained unauthorized access to agency documents during the course of the Intelligence Committee's years-long investigation into the detention and interrogation program."

Sen. Dianne Feinstein, who oversees the Intelligence Committee and has strongly supported the Snowden-revealed spying operations carried by the NSA and CIA, confirmed to the Times that an investigation into the matter was underway.

"Our oversight role will prevail," she said.

[Image of CIA Director John Brennan via AP]