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The leaders of the panel that independently reviewed last year's deadly attack on the U.S. diplomatic mission in Benghazi, Libya, said Tuesday they were prepared to testify publicly before Congress to counter what they consider unfounded criticism of their work.

In a letter to the House Oversight and Government Reform Committee, veteran diplomat Thomas Pickering said he and former Joint Chiefs Chairman Adm. Mike Mullen would answer any questions lawmakers have. Rep. Darrell Issa, R-Calif., chairman of the panel, is pressing for the two men to agree to an interview with staff investigators prior to a public hearing.

The work of the Accountability Review Board is the latest focus of a broader Republican inquest into their claims that the Obama administration misled Congress and the American people after the Sept. 11, 2012, attack that killed Ambassador Chris Stevens and three other Americans.

The blistering report released in December by Pickering, Mullen and three other reviewers found that "systematic failures and leadership and management deficiencies at senior levels" of the State Department meant security was "inadequate for Benghazi and grossly inadequate to deal with the attack that took place."

Pickering, however, noted how recently "some have called into question the integrity of the board and its work."

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"We believe that such criticisms are unfounded and, if left unaddressed, undermine the essential work that the board has done," he wrote. "It is therefore important that we be afforded the opportunity to appear at a public hearing before the committee and answer directly questions regarding the board's procedures, findings and recommendations."

Republicans believe the report was flawed, and they want to know why top officials like Secretary of State Hillary Rodham Clinton weren't interviewed. The panel absolved Clinton of any wrongdoing, faulting lower level State Department officials. Four were given paid suspensions.

On Monday, Issa asked Pickering and Mullen to meet privately with committee staff investigators to answer questions about their review. Democrats countered that if lawmakers wanted to talk to them, Issa should hold a full open hearing.

Pickering said the board "conducted a thorough review and produced a report that included detailed findings and frank and often highly critical assessments." It issued 29 recommendations for improving security at diplomatic facilities worldwide, and Pickering insisted that the board "fulfilled its role in identifying the lessons that must be learned and acted upon from Benghazi."

"We stand behind the board's report and look forward to discussing it in a public hearing," he wrote.

Frederick Hill, a spokesman for the committee, said late Tuesday that the panel was following up with Pickering and the State Department to determine whether he would appear voluntarily for an interview with committee staff investigators. Hill noted that Issa and Pickering appeared on a Sunday talk show together two days ago, and said the former diplomat had told the committee chairman that he would voluntarily submit to an interview.

"The committee is giving him a full opportunity to voluntarily follow through on his commitment," Hill said.

Issa, in his letter on Monday to Pickering and Mullen, had said that following the private interview, the committee would work with the report's authors on a date for a public hearing.