WASHINGTON — In a major shot to the administration, U.S. Sen. Mark Udall on Thursday demanded the resignation of CIA Director John Brennan in response to a new watchdog report that concluded that CIA officers improperly accessed computer files and records used by the Senate Intelligence Committee.

Udall, D-Colo., called for his dismissal after a classified briefing Thursday on the report, which was prepared by the CIA’s inspector general. Afterward, he said reports that CIA officers had spied on the Senate as it looked at the agency’s interrogation tactics were the latest example of the “tremendous failure of leadership” at the U.S. spy agency. Udall is a member of the Intelligence Committee.

“After being briefed on the CIA Inspector General report today, I have no choice but to call for the resignation of CIA Director John Brennan,” Udall said in a statement. “The CIA unconstitutionally spied on Congress by hacking into Senate Intelligence Committee computers. This grave misconduct not only is illegal, but it violates the U.S. Constitution’s requirement of separation of powers.”

The document, released Thursday by the CIA, is a summary of an internal CIA investigation that prompted Brennan to apologize to Senate Intelligence Committee leaders.

Brennan has convened an internal accountability board chaired by former Sen. Evan Bayh, D-Ind., that will examine whether the CIA officers should be disciplined, said his spokesman, Dean Boyd.

The agency officers searched Senate computers without permission for information gathered in the course of a Senate investigation into the CIA’s interrogation techniques. The summary of a classified report on post-9/11 detentions and interrogations that accuses the CIA of misconduct is expected to be made public soon.

Five agency employees improperly accessed Senate computers in an effort to track down certain documents, the inspector general found. Then, after Brennan ordered a halt to the review, the CIA office of security began a “limited investigation” that led to surveillance of Senate e-mails, the report said.

Sen. Dianne Feinstein, the California Democrat who chairs the Senate panel, said in a statement: “The investigation confirmed what I said on the Senate floor in March — CIA personnel inappropriately searched Senate Intelligence Committee computers in violation of an agreement we had reached, and I believe in violation of the constitutional separation of powers.”

The CIA conducted its search after it began to suspect that Senate aides had obtained a draft internal review that the CIA believed the Senate was not entitled to see. The review included comments from CIA officers describing misgivings about the treatment of al-Qaeda detainees.

As it turned out, the Senate staffers got the review thanks to a glitch in the CIA’s firewall, several officials said.

Udall’s criticism was echoed by rival U.S. Rep. Cory Gardner, who this year is challenging the first-term senator for his seat. The Yuma Republican did leave some wiggle room for Brennan.

“If the allegations are true and Director Brennan played any role in facilitating this breach of separation of powers, he must immediately resign,” Gardner said in a statement. “In addition, anyone from the agency that misled the public should be fired and investigated for potential criminal wrongdoing.”

U.S. Senate Majority Leader Harry Reid, D-Nev., expressed outrage.

“The CIA Inspector General’s report describes actions by the CIA that are appalling and deeply threatening to our system of checks and balances,” Reid said in a statement. “Congress has a constitutional responsibility to conduct oversight and the CIA’s actions were an attempt to undermine that responsibility.

“What is even more disturbing is that the unauthorized CIA actions come in the context of the Senate’s effort to complete a report of the CIA’s interrogation program. The deeply troubling CIA actions show to what lengths some in the CIA are willing to stoop in order to prevent the report’s release and to avoid accountability.”

Mark K. Matthews: 202-662-8907, mmatthews@ denverpost.com or twitter.com/ThewsDC

The Associated Press contributed to this report.