In a letter dated Wednesday to CIA Director John Brennan, Reid challenged the spy agency head's complaints that committee staff improperly accessed the agency's computers to obtain the documents, calling the allegation "patently absurd."
Last week, the head of the committee, Sen. Dianne Feinstein of California, questioned whether the agency broke the law and violated the Constitution in searching a computer network exclusively established for the committee.
Brennan has dismissed Feinstein's complaints.
Determined to resolve the fight, Reid said he had "instructed the Senate Sergeant-at-Arms (Terrance W. Gainer) to initiate a forensic examination of the computers and computer network assigned for exclusive (committee) use, in order to determine how the 'Panetta review' entered into the (committee) network."
The committee is close to completing a 6,000-page report on the CIA's brutal interrogation tactics, including waterboarding, at secret sites after the terrorist attacks of Sept. 11, 2001.
The CIA had established an exclusive computer network for committee staff in northern Virginia. In the course of the panel's investigation, the committee staff obtained documents from a review ordered by former CIA Director Leon Panetta and apparently took those documents to the Capitol.
"I understand that you have alleged that Senate Committee staff illicitly accessed classified CIA networks to obtain a document — the so-called 'Panetta Review' — which appears to corroborate the findings and conclusions of the committee's study and to contradict the CIA's own official response to the study," Reid wrote Brennan. "To my knowledge, the CIA has produced no evidence to support its claims that Senate committee staff who have no technical training somehow hacked into the CIA's highly secure classified networks, an allegation that appears on its face to be patently absurd."
Reid cited Brennan's Jan. 27 letter to Feinstein in which he said he would welcome an independent review. Reid asked Brennan to ensure that CIA personnel refrain from further interaction with committee staff on the issue, with the exception of the sergeant-at-arms staff. Reid also requested the appropriate security clearances for Gainer.
Gainer oversees Capitol security, heading a force of about 1,000.
Reid commented briefly on the dispute last week. The instructions to Gainer and the notification to Brennan ratcheted up a clash that pits Senate Democrats, led by Feinstein, against President Barack Obama's head of the spy agency.
Reid wrote to Brennan of the "grave and unprecedented concerns with regard to constitutional separation of powers this action raises."
Reid sent a copy of his letter to Attorney General Eric Holder. In the war of words between the agency and the Senate, the acting general counsel of the CIA has referred the matter to the Justice Department. The CIA's independent inspector general also has referred the issue to Justice.
Holder said Wednesday the department is reviewing the referrals.
Feinstein's dispute was sparked by fighting between Senate investigators and the CIA over a committee report on harsh interrogations. The report, which is still classified, concludes the CIA's use of coercive questioning was torture and produced little useful intelligence. The CIA argues the methods yielded important intelligence leads.
Senate aides reviewing classified computer files overseen by the agency have accused the CIA of monitoring their searches and withdrawing hundreds of internal documents without explanation. CIA officials blamed the aides for improperly accessing and mishandling classified files.
Both sides have claimed laws were broken. Brennan warned Feinstein in the January letter of a security breach caused by the aides; Feinstein accused the CIA last week of "a potential effort to intimidate this staff."
The committee is planning to vote next week on declassifying a 400-page summary of its report on harsh interrogations used during the war on terror, according to a government official. If approved, a CIA unit dedicated to line-by-line declassification will review the document, a process that also will involve lawyers from the CIA general counsel's office.
The committee is pressing for White House involvement and oversight of the process to ensure that any CIA official who was part of the interrogation unit doesn't have a say in what is declassified.
The official was not authorized to discuss the private talks and spoke on condition of anonymity.
Since Feinstein's remarkable broadside against the agency last week, the committee and the spy agency have continued contacts, focusing mostly on the declassification process.
The Associated Press obtained a copy of Reid's letter to Brennan.
Associated Press writer Stephen S. Braun contributed to this report.
Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.