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Four State Department officials have been "relieved from their duties" after an internal investigation of the Benghazi consulate attack found "systemic failures and leadership deficiencies at senior levels in securing the compound," prior to and during the assault, a State Department spokeswoman said.

An Accountability Review Board appointed by Secretary of State Hillary Clinton in September found that senior officials in the Diplomatic Security and Near East Affairs bureaus displayed management deficiencies that left security for the consulate, "inadequate for Benghazi and grossly inadequate to deal with the attack that took place."

The Sept. 11, 2012, attack resulted in the deaths of four Americans, including the U.S. ambassador to Libya, Christopher Stevens.

"The ARB identified the performance of four officials, three in the Bureau of Diplomatic Security and one in the Bureau of Near East Asia Affairs," spokeswoman Victoria Nuland said in a statement. "The secretary has accepted Eric Boswell's decision to resign as assistant secretary for Diplomatic Security, effective immediately. The other three individuals have been relieved of their current duties. All four individuals have been placed on administrative leave pending further action."

A State Department official confirmed to ABC News that all four officials remained employees of the State Department and had only been relieved of their current duties, pending further review.

A U.S. official confirmed to ABC News that along with Eric Boswell, who is the assistant secretary of state for diplomatic security, Charlene Lamb, the deputy assistant secretary responsible for embassy security, as well as an official with the Bureau of Near East Affairs, had also resigned "under pressure." Nuland did not specify any other resignations beyond Boswell's in the statement.

Ambassador Thomas Pickering headed the five-member Accountability Review Board, appointed by Clinton in September to investigate the attack. He told reporters at a briefing on Wednesday that State Department officials in Washington did not provide the security that the officials on the ground in Libya needed or deserved.

"The U.S. security personnel in Benghazi were heroic in their efforts to protect their colleagues, including Ambassador Stevens," Pickering said. "They did their best that they possibly could with what they had. But what they had was not enough, either for the general threat environment in Benghazi, and most certainly against the overwhelming numbers of attackers and the weapons which they faced.

"Frankly," he added, "the State Department had not given Benghazi the security, physical and personnel resources it needed."

The report did not name any individual as having been derelict in duty. But, Pickering said, the board not calling for specific disciplinary action did not reflect approval of performance, but rather the legal parameters it faced on recommending termination. Under the law and State Department policies, an official must have shown "willful misconduct," to be disciplined or terminated.

One of the board's recommendations from the Benghazi case was that, in the future, that policy be reviewed to allow more flexibility.

"There is such a large gap between willful misconduct, which leads, obviously, to conclusions about discipline, letters of reprimand, separation, the removal of an individual temporarily from duty - that we believe that gap ought to be filled," said Pickering.

"We found, perhaps, close to, as we say in the report, breach," he said. "But there were performance inadequacies, and those are the ones that we believe ought to be taken up. And we've made recommendations to the secretary in that regard."

Pickering did not characterize exactly what those recommendations were, but he said the board laid the blame for the security flaws on Washington bureaucrats at the assistant secretary level, "where the rubber hits the road."

Secretary Clinton stressed individual accountability in her response letter to Congress. From now on, she said, regional assistant secretaries based in Washington at the highest levels will be directly responsible and accountable for their people and posts in the field.

"Ambassadors are charged by the president to 'take direct and full responsibility' for the security of all personnel under their authority 'whether inside or outside the chancery gate,'" said Clinton. "The leadership of our regional bureaus will be embracing the same accountability and responsibility for the staff serving in these areas."

This post has been updated.