House Intelligence Committee Chairman Devin Nunes has accused the Department of Justice of "obstruction" and using "an array of tactics" to withhold key documents related to the FBI's use of a spy against the Trump campaign.

The spy in question is Stefan Halper, a 73-year-old Cambridge professor, former U.S. government official and longtime spook for the CIA and FBI - whose ex father-in-law was Ray Cline, former Deputy Director of the CIA.

Halper was outed as the FBI informant who infiltrated the Trump campaign to conduct espionage after the Washington Post and the New York Times ran reports that corroborated a March report by the Daily Caller. The Caller detailed Halper's outreach to several low-level aides to the Trump campaign, including Carter Page, George Papadopoulos, and a cup of coffee he had with campaign co-chair Sam Clovis.

In a Friday letter to Deputy Attorney General Rod Rosenstein, Nunes accused the DOJ of refusing to turn over key documents concerning the agency's use of Halper.

"DOJ continues to obfuscate and delay its production using an array of tactics, such as incorrectly categorizing the requested documents as Gang-of-Eight-level material in order to limit access," wrote Nunes, in reference to an April 30 subpoena for the documents. "Such conduct by DOJ is unacceptable because the Gang-of-Eight is a legal fiction that has no basis outside of the confines of Presidential approval and reporting of covert actions."

Nunes added "Your continued refusal to permit Members of Congress and designated staff to review the requested documents is obstruction of a lawful Congressional investigation."

Rosenstein appears nonplussed at the letter - with a DOJ official commenting to Fox News that the Deputy AG is busy with other matters, and will plan to respond during a previously scheduled briefing on Thursday.

“He, along with the FBI Director and DNI Coats, look forward to further briefing and again presenting responsive documents to Chairman Nunes and the rest of his colleagues in the Gang of 8 meeting scheduled for Thursday of this week,” the official said.

Nunes' letter was in response to an offer by the Justice Department and the FBI to brief the "Gang of Eight" in an effort to blunt criticism from the House conservatives who repeatedly have pressed for documents and questioned the department's conduct in the Russia investigation. The Justice Department originally denied Congress access to any of the documents, citing national security concerns. But it later relented and held two high-level briefings last month in response to pressure from the White House, Nunes and House Speaker Paul Ryan, R-Wis. -Fox News

The DOJ official said last week that the agency would provide new materials and that "the documents that were available for review but not inspected by the members at the previous briefing."

"Frankly the sooner the Department of Justice complies with all of our document requests, which are legitimate document requests, the better this is going to be for everybody, and had they complied with the document requests earlier when we made them, we probably could have spared the country of all of this drama," Ryan said Thursday.

"I will not relent in my duties on behalf of the American public to discover all the facts in this matter," Nunes concluded in his letter. "Any response falling short of this request will be considered an effort to conceal material information from Congress -- a dangerous precedent that threatens the core of our democracy."