The CIA searched computers intended to be used solely by the Senate Intelligence Committee in an apparent effort to determine how committee staff members gained access to a draft version of an internal agency review of its controversial interrogation program, U.S. officials said.

The action, some officials say, would mark the first time a U.S. intelligence agency has accessed congressional computers and would be an apparent violation of the constitutional principle of separation of powers.

The CIA notified the committee of the search after the fact, and some lawmakers believe that the agency violated federal law, according to officials familiar with the matter.

The CIA’s inspector general has begun an investigation into the conduct of agency employees, and a referral has been made to the Justice Department to see whether there are grounds for a criminal inquiry, officials said.

“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,” CIA Director John O. Brennan said in a statement Wednesday. “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. Until then, I would encourage others to refrain from outbursts that do a disservice to the important relationship that needs to be maintained between intelligence officials and Congressional overseers.”

Committee Chairman Dianne Feinstein (D-Calif.) on Tuesday confirmed the existence of the investigation, which was first reported by McClatchy newspapers and the New York Times.

Democratic committee members have pressed for release of the agency review, whose findings, they said, apparently are consistent with the panel’s own conclusions in a still-classified 6,300-page report on the CIA’s now-defunct interrogation and detention program. The committee’s report, according to people who have read it, found that harsh interrogation tactics used against al-Qaeda detainees failed to produce significant intelligence, and that the agency in some cases misled Congress and the public about the value of those tactics, including waterboarding.

In a 122-page rebuttal to the committee’s study issued last June, Brennan challenged specific findings and the report’s overall conclusion about the program’s value. That document is still classified.

The revelation in December by Sen. Mark Udall (D-Colo.) of the existence of the internal review, which Udall said “amazingly . . . conflicts with the official CIA response,” apparently angered the agency, officials said.

“The CIA tried to intimidate the Intelligence Committee, plain and simple,” Udall told reporters Wednesday, according to Roll Call. “I’m going to keep fighting like hell to ensure that the CIA never dodges congressional oversight again.”

The internal review, Udall said at a December hearing, “raises fundamental questions about why a review the CIA conducted internally years ago and never provided to the committee is so different from the CIA’s formal written response to the committee’s study.”

The review, also described as a summary, was initiated by Brennan’s predecessor, Leon E. Panetta.

Udall alluded to the CIA’s computer searches in a letter to President Obama on Tuesday, saying, “As you are aware, the CIA has recently taken unprecedented action against the committee in relation to the internal CIA review.”

Udall pressed the White House to make a public statement in support of declassification of the committee’s report and to release the final version of the internal CIA review.

Much of the work on the study, which cost $40 million and began in 2009, was done in a secure facility leased by the CIA in Northern Virginia. In an unusual arrangement, the agency set up computers in a locked room to which only the committee would have access, according to officials and court documents.

CIA documents were transferred to the secure system, including, apparently, a version of the internal review, officials said.

The CIA created “a segregated” network drive that allowed the committee to “prepare and store [its] work product,” in a secure environment, according to a document filed in litigation over the report’s release.

“One key principle” in this arrangement was that the materials created by the committee “are the property of the committee” and “remain congressional records in their entirety,” said Neal Higgins, the CIA’s director of congressional affairs, in a declaration filed in response to a lawsuit by the American Civil Liberties Union seeking the report’s release.

Sari Horwitz and Julie Tate contributed to this report.