Four State Department managers were disciplined Wednesday, following sharp criticism from independent investigators that the department did not do enough to protect a group of Americans killed in an eight-hour siege in September of U.S. government compounds in Benghazi, Libya.

The highest-ranking official, Eric Boswell, the head of the Diplomatic Security Bureau, resigned effective immediately, the State Department announced late Wednesday. The three others were responsible for various aspects of embassy security and planning for Libya and the Middle East.

They were relieved of their responsibilities and were expected to be reassigned, said a senior administration official, who spoke on the condition of anonymity. The official was not authorized to discuss the matter publicly.

Despite the fallout, Republicans who have criticized the Obama administration’s handling of the Benghazi attack called the inquiry tepid and the recommendations for punishment inadequate.

Rep. Mike Rogers (Mich.), chairman of the House intelligence committee, said the three-month investigation steered clear of holding senior State Department officials accountable for the deaths of the four Americans, including the U.S. ambassador to Libya.

Document: Sec. Clinton’s letter to Senate Foreign Relations Committee

“You’d think the whole purpose would be to be harshly critical of mistakes so you don’t make them again,” Rogers said.

Although the State Department released an unclassified version of the Benghazi report, its authors and others familiar with the investigation said the classified version described in greater detail intelligence failures that contributed to the Sept. 11 attack. The lengthy report paints a picture of inadequate information and difficulty sharing it within the department.

“We found that there was no immediate tactical warning of the September 11 attacks, but there was a knowledge gap in the intelligence community’s understanding of extremist militias in Libya and the potential threat they posed to U.S. interests,” said retired Adm. Mike Mullen, a former chairman of the Joint Chiefs of Staff and a co-author of the report.

He added: “Increased violence and targeting of foreign diplomats and international organizations in Benghazi failed to come into clear relief against the backdrop of ineffective local governance, widespread political violence and inter-militia fighting, as well as the growth of extremist camps and militias in eastern Libya.”

The Accountability Review Board found that Ambassador J. Christopher Stevens had unusual latitude to make security and travel decisions, and that he did not always keep his superiors informed. The report squarely blamed terrorists for the assault and did not identify any single failure on the part of U.S. officials that might have prevented it.

“The U.S. security personnel in Benghazi were heroic in their efforts to protect their colleagues, including Ambassador Stevens. They did their best that they possibly could with what they had, but what they had was not enough,” said former U.S. ambassador Thomas R. Pickering, a co-author.

He said the panel fixed blame or responsibility at the level of State Department assistant secretary, “where the decision-making in fact takes place, where, if you like, the rubber hits the road.”

Assistant secretaries head the various bureaus, or sections, which are divided by geographic region and function.

The State Department declined to identify the three officials besides Boswell who were disciplined. But the senior administration official identified two of them as Charlene Lamb, the deputy assistant secretary responsible for embassy security, who testified to Congress in October that the diplomatic mission in Benghazi had the appropriate level of security on the night of the attack, and Raymond Maxwell, a deputy assistant secretary in the Bureau of Near Eastern Affairs.

The third, who has not been identified, works in the Diplomatic Security Bureau.

The panel tasked with investigating the attack did not have the authority to recommend that employees be terminated, but it was permitted to determine whether employees were derelict in their duties. Pickering said none of the management failures rose to that level.

The report also does not fault Secretary of State Hillary Rodham Clinton directly. She received a copy of the classified report earlier this week and has told Congress that she accepts its findings. The House Foreign Affairs Committee said Wednesday that she will testify before the panel by mid-January, after having been forced to cancel her scheduled testimony because of an illness.

“We have learned some very hard and painful lessons in Benghazi,” said Deputy Secretary of State William J. Burns, who will testify in Clinton’s place. “We are already acting on them. We have to do better.”

Clinton said she will work to address the panel’s 29 recommendations. Five of them were not included in the unclassified version of the report, and Pickering said they mostly concern classified intelligence matters. At least one also deals with recommended discipline for managers found at fault.

Among other recommendations, the five-member panel suggested an overhaul of intelligence-sharing procedures within the State Department “to get key security-related threat information into the right hands more rapidly.”

Although the report says there was a general lack of understanding of the threats in Benghazi, the criticism is aimed mostly at the State Department’s use of the intelligence it had. The CIA, a major player in the U.S. operation in Benghazi, is never mentioned in the unclassified report.

“Across the board, what we’re talking about here is how intelligence information was used,” a senior U.S. intelligence official said. “It’s a question of how a particular agency views that information and connects the dots.”

The report’s sharpest criticism, including recommendations not released to the public, was aimed at the State Department’s threat analysis unit, which is criticized for being too focused on searching for specific warnings of pending attacks to notice broader signs that the danger level was rising.

Alluding to a CIA compound in Benghazi that came under attack but was never overrun, Rogers said that “would certainly beg the question of why did one have appropriate protection” while the State Department facility did not.

The CIA, the Office of the Director of National Intelligence and others had been waiting to see whether the report would identify shortcomings in their role in Benghazi. But officials said the report’s criticism is confined to the gaps in U.S. spy agencies’ understanding of militant groups.

“What we were looking for is are there any criticisms of the intelligence we’re providing or the way that we’re providing it, and the answer to that thus far is no,” the U.S. intelligence official said.

The report identifies shortcomings in the U.S. understanding of militias in Benghazi, including the group known as Feb. 17 that had been hired by the State Department but did not respond to pleas for help during the attack.

“It is a very loose group of local militias that float in and out of that umbrella over time,” Mullen said. “I think that’s representative of the gaps, the intelligence gaps that existed at that time in eastern Libya broadly, not just for us but for many countries that were out there.”

Rep. Adam B. Schiff (D-Calif.), a member of the House intelligence committee, said the poor understanding of overlapping militia memberships, competing agendas and rogue elements “caused us to put a misplaced reliance on them for security.”

Karen DeYoung contributed to this report.