A State Department-ordered investigation into September's attack on the U.S. Consulate in Benghazi, Libya, concluded that "systemic failures" left the facility inadequately protected, according to the independent review board's report, which confirmed that no protest preceded the deadly attack.

The report, posted Tuesday night on the State Department's website, also identified "leadership and management deficiencies at senior levels within two bureaus." It suggested 29 ways the department can improve its operations, but recommended no disciplinary action.

The Accountability Review Board's report comes after more than three months of intense debate in Washington over who was behind the attack, what motivated the attackers and why U.S. authorities weren't able to stop the violence, which took the lives of Ambassador Christopher Stevens and three other Americans.

Republicans have accused Obama administration officials of giving the American people a series of misleading explanations for the attack from the start. Much of the criticism focused on U.N. Ambassador Susan Rice's comments five days after the Sept. 11 attack that the violence was a "spontaneous" result of protests against an anti-Islam film. She later backtracked, saying her comments were based on the most current information provided by the intelligence community.

Although the motive for the attack remains unclear, the report released Tuesday confirms what quickly became evident -- that the attack was the coordinated work of heavily armed terrorists.

The report confirmed that the attack involved "arson, small arms and machine gun fire, and the use of RPGs, grenades, and mortars."

The security failures, though, were singled out repeatedly in the report.

Despite clear and present threats, the review board found the security staffing at the Benghazi consulate was "short-term, transitory" and "relatively inexperienced" -- and ultimately "inadequate."

It also found "a pervasive realization among personnel who served in Benghazi that the Special Mission was not a high priority for Washington when it came to security-related requests, especially those relating to staffing."

Clinton vowed Tuesday to address the deficiencies identified in the report.

"The Accountability Review Board report provides a clear-eyed look at serious, systemic challenges that we have already begun to fix. I am grateful for its recommendations for how we can reduce the chances of this kind of tragedy happening again. I accept every one of them," Clinton said in letters to the Senate and House panels reviewing the attack.

Although much of the focus is on the State Department's preparedness, the review board didn't let Libyans off the hook. Some of the security was provided by a militia, and there were "some troubling indicators of its reliability in the months and weeks preceding the September attacks," the report said.

The review board "found little evidence" that the guards provided by the militia "offered any meaningful defense" of the compound.

Among the board's recommendations for the State Department are to strengthen its security detail in high-risk posts, to build more-secure facilities, to request the support of additional Marines and to step up security training.

The report also gives a detailed description of the attacks, which the report said "were unanticipated in their scale and intensity."

At one point, the report says, U.S. officials were unable to find Ambassador Stevens "for several hours." Then they received a call from a cell phone Stevens had been carrying. An Arabic-speaking man said there was an unresponsive man matching Stevens' description at the hospital.

At first there was concern that this call was an attempt to lure U.S. personnel into a trap, but they later confirmed that Stevens was at the Benghazi Medical Center and had died after being caught in the fire at the consulate.

The report, however, shoots down criticisms that the U.S. military should have been called in sooner to help.

"The interagency response was timely and appropriate, but there simply was not enough time given the speed of the attacks for armed U.S. military assets to have made a difference," the report says.

The board, though, determined the Libyan government's response that night was "profoundly lacking."

Lawmakers generally praised the review board after the report's release, but reserved tough words for the State Department and other agencies.

"The report makes clear the massive failure of the State Department at all levels, including senior leadership, to take action to protect our government employees abroad," House Intelligence Committee Chairman Mike Rogers, R-Mich., said in a statement.

Further, he said the U.S. is "on the verge of compounding these errors by not acting against those involved in the attacks," complaining of a "lack of progress" in pursuing the terrorists responsible.