State Department officials on Tuesday began backing away from earlier accounts made by others in the Obama administration regarding last month’s attack on the U.S. diplomatic mission in Benghazi, Libya.

Officials who spoke to the media on condition of anonymity said the department never concluded the Benghazi attack, which claimed the lives of four Americans including Ambassador Chris Stevens, was the escalation of protests against the American-made anti-Islam “Innocence of Muslims” YouTube video.

Representatives from the State Department are expected to go before congressional lawmakers Wednesday for a hearing on the Sept. 11 incident. (You can watch the hearing here at noon.)

State Department spokeswomen Victoria Nuland on Wednesday said that the representatives were specifically requested by the Committee on Oversight and Government Reform. They are Eric Nordstrom, who was head of diplomatic security in Libya until June, and Charlene Lamb, deputy assistant secretary in the Bureau of Diplomatic Security. They will be joined by Ambassador Patrick Kennedy, undersecretary of management, and Lt. Col. Andrew Wood, a Utah National Guard Army Green Beret, who headed a Special Forces “Site Security Team” in Libya.

Besides saying that the Benghazi incident happened without any warning, officials told the Associated Press that reaction forces quickly rushed to the scene and conducted an evacuation under heavy gunfire that spilled onto the streets.

Those officials also told the AP that Ambassador Stevens had meetings on and off the consulate compound the day prior to the attack, but spent Sept. 11 on site. There were five U.S. agents and four local men securing the compound that day, according to the AP.

When gunfire broke out later that day, Stevens and others were escorted to a safe room in the compound. The intruders couldn’t break into Stevens’ safe haven, so they threw fuel cans in the building and lit it on fire. Stevens tried to escape but didn’t make it out, dying of smoke inhalation.

Other officials told ABC News that they have never seen an attack of this type and magnitude in Libya.

“The lethality and number of armed people is unprecedented," they said. “There was no attack anywhere in Libya -- Tripoli or Benghazi -- like this, so it is unprecedented and (it) would be very, very hard to find a precedent like that in recent diplomatic history.”

In addition, reports are that there were no protests before the attack on the compound and that former Navy SEALs Glen Doherty and Tyrone Woods died as a result of a mortar attack. It is still unclear how Stevens made it from the compound to the hospital, according to ABC News, as security officials didn't see him until his body was delivered to the airport.