The size and "lethality" of the attack on the U.S. consulate compound in Benghazi, Libya, that left Ambassador Chris Stevens and three other Americans dead was "unprecedented," a senior State Department official said today.

Senior State Department officials today gave the most detailed account to-date of the attack on the U.S. consulate in Benghazi on Sept. 11, which killed Ambassador Chris Stevens and three other diplomats. One official said the nature of the assault was unparalleled in recent history.

"The lethality and number of armed people is unprecedented," one of the officials said. "There was no attack anywhere in Libya -- Tripoli or Benghazi -- like this, So it is unprecedented and would be very, very hard to find a precedent like that in recent diplomatic history."

Though the timeline of events outlined on the call was similar to the last official account of the incident, which was given on Sept. 12, some stark differences and new details were revealed.

The biggest difference was a clear statement that there were no protests before the attack. Also it was revealed that former Navy SEALs Glen Doherty and Tyrone Woods died from a mortar attack and that officials still do not know how Stevens, who was suffering from severe smoke inhalation, made it from the compound to the hospital.

The officials gave a vivid narrative of the events of the night, painting a picture of exactly what the compound looked like.

There were four buildings in the main compound, according to the State Department's narrative: The barracks where the local guards were housed; Building C, which is the main building that contained Stevens residence; Building B, a building on the compound; and the TOC (Tactical Operations Center) that served as the main security and communications center for the compound.

The area of the compound was about the size of a football field, with a nine-foot-high wall, topped by three feet of barbed wire.

On Sept. 11, Stevens did not leave the compound because of security fears due to the 9/11 anniversary. He had arrived in Benghazi the day before with five guards in total. Two additional Diplomatic Security agents from Tripoli were with him in addition to the three agents normally detailed to the compound.

Though some administration officials had initially said that the attack grew out of protests over an anti-Muslim film, the senior State Department official told reporters today that "nothing was out of the ordinary" on the night of the attack.

At 8:30 p.m., the ambassador said goodnight to a visiting Turkish diplomat outside the compound and the streets were empty. But at 9:40 p.m., noises, gunfire and an explosion were heard by the agents located in the TOC and Building B.

The agent in the TOC looked at one of the camera feeds monitoring the perimeter and saw a large group of armed men entering the compound. Asked about the initial reports of the protests, the official said that while "others" in the administration may have said there were protests, the State Department did not.

"That was not our conclusion," the official said. "I'm not saying that we had a conclusion."

This starts a series of events during which Stevens, Information Specialist Sean Smith and the agent locked themselves in a safe area in Building C. The area is set aside from the rest of the building by a metal grille with several locks and contained a small room with water and medical supplies.

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