By Andrew Quinn and Phil Stewart
WASHINGTON, Sept 12 (Reuters) - Security personnel were separated from the U.S. ambassador to Libya during the attack in which he was killed, U.S. officials said on Wednesday, describing a chaotic scene of smoke, gunfire and confusion as the American consulate in Benghazi came under assault.
The officials said the attack began at roughly 10 p.m. local time on Tuesday, with U.S. Ambassador Christopher Stevens, information technology specialist Sean Smith and one security officer trapped under fire in the burning consulate building.
"They became separated from each other due to the heavy dark smoke while they were trying to evacuate the burning building," one senior official said, who spoke on condition of anonymity and stressed that it was a preliminary version of events.
The security officer made it outside, and returned with help to search for the missing U.S. diplomatic personnel.
"At that time, they found Sean. He was already dead. And they pulled him from the building. They were unable, however, to locate Chris (Stevens), before they were driven from the building, due to the heavy fire and smoke and the continuing small arms fire," the official said.
During the next several hours, U.S. and Libyan security forces exchanged repeated gunfire with the attackers, whom they identified as Libyan extremists.
The description of events at the consulate, while preliminary, appeared to raise questions about security preparations and procedures.
A second U.S. official said there were no U.S. military personnel at the mission in Benghazi at the time of the attack.
Questioned about the consulate's security, the officials said the consulate compound was guarded by both Libyan security and a "robust" force of U.S. security officers, and that a regular security review before the anniversary of the Sept. 11, 2001, attacks had recently been completed.
"And at that point, there was no information and there were no threat streams to indicate that we were insufficiently postured," the first U.S. official said.
U.S. and Libyan security forces eventually were able to secure the consulate complex, and shepherd several dozen consular staff to a nearby safe haven. But the fate of the 52-year-old ambassador remained unclear.
"At some point in all of this, and frankly we do not know when, we believe that Ambassador Stevens got out of the building and was taken to a hospital in Benghazi. We do not have any information on what his condition was at that time," the first official said.
Stevens' body was later returned to U.S. custody at Benghazi airport, where it was evacuated along with the rest of the personnel to Tripoli, the U.S. official said.
Two other embassy personnel were also killed in the attack, but have not been identified pending notification of their families, the official said. Three more people were wounded.
The official was unable to confirm media reports that unidentified Libyans had found Stevens and brought him to the hospital.
"Obviously he had to get there somehow. No Americans were responsible for that. But again I'm not in a position to confirm, because we frankly don't know," the official said.
The official declined to discuss specifics of Stevens' security detail, but defended their efforts.
"I think in the accounting that I gave I made clear that security personnel were endeavoring to get him out of the building when they got separated by the incredibly thick smoke and fire," the official said.
"They then turned right back around, got more help and went right back to look for him. So this was realty quite a heroic effort."
Following the attack, the United States evacuated all its personnel from Benghazi to the Libyan capital and has reduced the staff at its embassy in Tripoli to unspecified "emergency" levels, the official said.
In response to the crisis, the Pentagon dispatched a team of about 50 members of the Marine fleet anti-terrorist security team, who were on the ground at the embassy in Tripoli.
The first official said that in addition to official Libyan security, a local militia friendly to U.S. interests had also joined the effort to defend the consulate.
The officials declined to speculate on whether al Qaeda might be involved, saying evidence from the attack was still under review.