They added that while intelligence officials indicated early on that extremists were involved in the assault, only later were officials able to confirm that the attack was not generated by a protest over the film.
The Associated Press has reported that the CIA station chief in Tripoli and a State Department official sent word to Washington during the attack citing eyewitnesses as saying it was not a film protest but the planned work of armed militants.
Sen. John McCain and other Republicans insist that if the Obama administration didn't know enough about the attack to discuss it clearly in the days that followed, it should have. They also say the response to the attack has been too muted to send a deterrent message to terrorists.
The officials' description Thursday of the attack provided details about a second CIA security team in Tripoli that quickly chartered a plane and flew to Benghazi but got stuck at the airport. By then, however, the first team had gotten the State Department staff out of the consulate and back to the CIA annex.
As the events were unfolding, the Pentagon began to move special operations forces from Europe to Sigonella Naval Air Station in Sicily. U.S. aircraft routinely fly in and out of Sigonella and there are also fighter jets based in Aviano, Italy. But while the U.S. military was at a heightened state of alert because of 9/11, there were no American forces poised and ready to move immediately into Benghazi when the attack began.
The Pentagon would not send forces or aircraft into Libya — a sovereign nation — without a request from the State Department and the knowledge or consent of the host country. And Defense Secretary Leon Panetta has said the information coming in was too jumbled to risk U.S. troops.
According to the detailed timeline senior officials laid out Thursday, the first call to the CIA base came in at about 9:40 p.m., and less than 25 minutes later about the team headed to the consulate. En route they tried to get additional assistance, including some heavier weapons, but were unable to get much aid from the Libyan militias.
The team finally got to the consulate, which was engulfed in heavy diesel smoke and flames, and they went in to get the consulate staff out. By 11:30 p.m., all of the U.S. personnel, except Stevens, left and drove back to the annex, with some taking fire from militants along the way.
By that time, one of the Defense Department's unarmed Predator drones had arrived to provide overhead surveillance.
At the CIA base, militants continued the attack, firing guns and rocket-propelled grenades. The Americans returned fire, and after about 90 minutes, or around 1 a.m., it subsided.
Around that time, the second CIA team, which numbered about six and included two military members, arrived at the airport, where they tried to figure out where Stevens was and get transportation and added security to find him.
Intelligence officials said that after several hours, the team was finally able to get Libyan vehicles and armed escorts, but by then had learned that the ambassador was probably dead and the security situation at the hospital was troublesome. The State Department has said a department computer expert, Sean Smith, also was killed.
The second CIA team headed to the annex, and arrived after 5 a.m., just before the base came under attack again.
According to officials, militants fired mortar rounds at the building, killing two of the security officers who were returning fire. The mortar attack lasted just 11 minutes.
And less than an hour later, a heavily armed Libyan military unit arrived and was able to take the U.S. personnel to the airport.
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