Updated

A leading U.S. congressman investigating the nation's largest Islamic advocacy group says he is "deeply disappointed" with an embarrassing reply he received from a letter he sent to the FBI.

Rep. Frank Wolf, R-Va., sent the letter on Feb. 2 after FOXNews.com report that the bureau had severed ties with the Council on American-Islamic Relations amid mounting evidence that the group was linked to a support network for Hamas.

The FBI severed its ties with all local chapters of CAIR after a 15-year investigation culminated with the conviction in December of Hamas fund-raisers. CAIR was listed as an unindicted co-conspirator in the case.

Wolf reached out to the FBI's assistant director for counterterrorism to find out whether the bureau still had any contact with the group it called a front for Islamic radicals, and whether CAIR was receiving funds from foreign sources.

After waiting more than a month, Wolf said, the only response he got was a four-paragraph letter from the FBI's head of public relations.

The response left the 15-term congressman seething -- and now he's pushing back.

"I would like these questions fully answered by this Friday, March 13, and by someone who works on counter-terrorism, rather than a public affairs officer," Wolf wrote in a follow-up letter this week. "I would think the Bureau would be embarrassed to send the insufficient response I received."

Click here to see Wolf's letter to the FBI.

Wolf, the ranking member of the appropriations subcommittee that oversees the FBI, told FOXNews.com he personally hand-delivered his response to the FBI on Monday. He said he is "one of the FBI's best friends in Congress" and expected timely and detailed responses to his questions.

"I was deeply disappointed with the FBI's response," Wolf wrote. "It took the Bureau more than a month to respond, and the letter I received provides only a partial answer to one of the 10 questions I posed."

Wolf is not the only member of Congress interested in CAIR's case; the House and Senate are both pushing the FBI to clarify its decision to ban contact with CAIR.

Members of the House anti-terrorism caucus have called on the FBI to assert their ban as a government-wide policy. Republican Reps. Sue Myrick and Patrick McHenry of North Carolina and Paul Broun of Georgia urged FBI Director Robert Mueller last week "to show other federal agencies the evidence the Department of Justice has on CAIR's terrorist ties in order to ensure that none of our federal agencies are working with this group."

Sens. Chuck Schumer, D-NY, and Jon Kyl, R-Ariz., pushed Mueller in the same direction. "Obviously, we believe this should be government-wide policy," they wrote in a February letter.

House staffers say they have not received replies from the FBI, but Wolf told FOXNews.com he's confident he'll hear back from the bureau by Friday.

"I do sure expect an answer," he said. "If I don't get an answer, why do we even have congressional oversight? We should just abolish the Congress."