(CNN) – The ongoing dispute over how and where to debate the independent review of last September's attack in Benghazi continued Friday with the subpoena of the review board's co-chair to be deposed by congressional investigators.
Thomas Pickering, a former ambassador, has said he would prefer to testify in a public hearing of the House Committee on Oversight and Government Reform rather than submit to a private interview, but the panel's chairman, Rep. Darrell Issa, wants the meeting behind closed doors before any open session.
"While I am very much committed to having you testify publicly and appreciate your newfound willingness to do so, I was disappointed that you are attempting to limit the Committee's understanding of the Accountability Review Board by refusing to participate in a voluntary transcribed interview prior to testifying publicly," Issa wrote to Pickering on Friday.
"In light of your continuing refusal to appear voluntarily for a transcribed interview, however, I have found it necessary to issue a subpoena to compel your appearance at a deposition."
Republicans, including Issa, have questioned the Benghazi Accountability Review Board's findings on the attack last September at an American diplomatic post in Benghazi, Libya, which left four Americans dead.
The report, issued late last year, found "systemic failures and leadership and management deficiencies" at the State Department in the lead-up to the attack in Benghazi. As a result, four State Department officials were disciplined immediately after the report's release. One resigned, while three others were placed on administrative leave and relieved of their duties.
But critics say the report did not go far enough, and did not include accounts from key witnesses to the attack who were on the ground as it happened.
The disparagement heated up earlier this month at a House Oversight Committee hearing featuring several witnesses who said they weren't interviewed by the review board.
Neither Pickering nor his co-chair, Admiral Mike Mullen, appeared at that hearing, leading to a bitter back-and-forth over whether they were invited to testify. The following weekend on NBC's "Meet the Press," Issa said he would request a deposition from Pickering and Mullen on how their panel reached its conclusions.
"Ultimately, if they got it right, we can put this issue to rest," Issa said. "We believe it was insufficient. We believe it's likely they did not interview all the people."
Pickering and Mullen responded to that request Wednesday, addressing a letter to Issa requesting a public hearing rather than a closed-door interview.
"The public deserves to hear your questions and our answers," they wrote.
Rep. Elijah Cummings, the highest ranking Democrat on the oversight panel, wrote in a statement Friday that Issa's subpoena was a "stark example of extreme Republican overreach and the shameful politicization of this tragedy."