On the eve of a grilling at Congress, the State Department hit back Tuesday at charges of security lapses in Libya, detailing a fierce attack on its Benghazi mission which it said erupted without warning.
Top officials are preparing to address Wednesday's first public congressional hearing into the September 11 attack in which the ambassador, Chris Stevens, and three other American diplomatic staff were killed.
In a dramatic, new account, two State Department officials described a relentless attack in which dozens of armed men invaded the US consulate in Benghazi, setting it on fire and hunting through the building for staff.
There had been no warning that an attack was planned, and in the hours before the streets outside the compound had been calm, they said on a conference call with reporters, asking to remain anonymous.
The new account contradicts initial reports by State Department officials which said it was a "spontaneous" attack sparked by a protest against an anti-Islam film.
"There was no actionable intelligence of any planned or imminent attack," one top State Department official said Tuesday.
Stevens held a series of meetings and stayed in the compound that day as it was the 11th anniversary of the September 11, 2001 attacks. He walked his last guest, a Turkish diplomat, to the compound gates.
"They say goodbye, they're out in the streets. Everything is calm, at 8:30pm there's nothing unusual, there has been nothing unusual during the day at all," a second official said.
Asked why initially State Department officials had said there had been a protest against the amateur video, the first official said that was a question "for others. That was not our conclusion."
The new timeline is sure to anger Republicans who have sought to skewer President Barack Obama on allegations of security and foreign policy lapses, ahead of the November 6 presidential elections.
Four US officials will brief lawmakers Wednesday at the hastily-arranged hearing of the Oversight and Government Reform committee -- the main watchdog in the Republican-controlled House of Representatives.
Leaked emails would seem to support charges that requests for more security were denied, and even Stevens's diary reportedly suggested he feared he was on an Al-Qaeda hit list.
Under Secretary for Management Patrick Kennedy, who oversees State Department management affairs and diplomatic security, will be one of the key witnesses.
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Charlene Lamb, deputy assistant secretary at the Bureau of Diplomatic Security, will also testify alongside regional security officer Eric Nordstrom.
The fourth witness is Lieutenant Colonel Andrew Wood, who was a leading member of special site security team set up by the Pentagon in Tripoli.
Wood told CBS news that he and other staff at the embassy "felt we needed more, not less" security personnel, but were told "to do with less. For what reasons, I don't know."
The first State Department official said Tuesday it was difficult to say what kind of security would have been needed to repel such an attack.
"The lethality and the number of armed people is unprecedented. There have been no attacks like that in Libya, Tripoli or Benghazi or elsewhere in the time that we have been there," the official said.
"It would be very, very hard to find a precedent for an attack like that in recent diplomatic history."
There were five US diplomatic security agents at the main compound -- two who had traveled with Stevens from Tripoli as well as three posted in Benghazi -- and four members of local Libyan security forces.
Gunfire and explosions first erupted around 9:40 pm and agents manning security cameras saw "a large number of armed men flowing into the compound," said one of the officials.
The armed attackers doused the outside of one of the buildings with diesel, setting it alight and then invaded the main residence, pouring fuel over furniture and starting a blaze, which let off plumes of thick, choking smoke.
An armed American security agent alerted Stevens, and together with US information manager Sean Smith they sheltered in a fortified safe haven, equipped with medical supplies and water, in a closet on the bedroom floor of of the main residence.
But the three men soon found it hard to breathe and after moving to a bathroom with a grilled window, decided they had to make a break for it despite tracer bullet fire and grenades raining around the compound inside.
In their bid to escape, the three were separated. Smith's body was found during heroic search attempts by US security while Stevens somehow was taken to a hospital and his body later returned to US diplomatic staff that night.
The remaining security forces fled through chaotic streets in an armored vehicle for a nearby annex, which then around 4:00 am also came under sustained mortar fire. Two US security agents were killed.
The annex was then evacuated, and all the staff, dead and wounded were flown in two flights back to Tripoli.