The Pentagon released Friday a timeline of the events that transpired on the night of Sept. 11 in Benghazi which stated that top U.S. defense officials were notified of the attack within an hour of the initial assault on the consulate but assistance could be mobilized only after another hour.

However, senior defense officials, who spoke to Reuters on condition of anonymity, rejected the criticism that the Pentagon failed to move quickly.

“The Department of Defense acted quickly after learning of the incidents unfolding in Benghazi," an official told Reuters, adding that Marines, special forces and other military assets had either been employed or put in motion during the attack. "Unfortunately, no alternative or additional aircraft options were available within a timeline to be effective," the official added.

According to the timeline, armed men began their assault on the U.S. Consulate in Benghazi Sept. 11 at 9:42 p.m. local time.

At 9:59 p.m., an unarmed U.S. surveillance drone was diverted to Benghazi in eastern Libya by the military's Africa Command, based in Europe, to assess the situation. However, the drone could arrive over the consulate only after another hour at 11:10 p.m.

The Office of the Secretary of Defense and the Joint Staff were notified of the attack by the National Military Command Center at the Pentagon at 10:32 p.m., 50 minutes after the initial assault began.  The information reached Secretary of Defense Leon Panetta and Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey shortly thereafter.

At 11 p.m., Panetta and Dempsey met with President Obama at the White House where they discussed potential responses to the attack on the diplomatic facility. The meeting had been previously scheduled.

By 11:30 p.m., almost two hours after the initial attack, all surviving U.S. personnel were evacuated from the consulate by a CIA ream that arrived from a nearby base. U.S. Ambassador Chris Stevens was missing.

Meanwhile, Panetta and Dempsey returned to the Pentagon and began to coordinate responses to the attack with General Carter Ham, head of Africa Command, and other senior military leaders. The series of meetings, which began at 12 a.m., went on till 2 a.m.

At 1:30 a.m., a six-man security team from the U.S. Embassy in Tripoli arrived in Benghazi.

The ambassador’s body was found at a local hospital. He died of asphyxiation in the smoke-filled diplomatic compound after it torched by the attackers. Computer expert Sean Smith was identified was the second casualty in the initial assault.

Panetta gave verbal orders for Marine anti-terrorist teams from Rota, Spain, to prepare to deploy to Tripoli and Benghazi. He also ordered special operations force team training in Croatia and an additional special operations force team in the U.S. to prepare to deploy to a staging base in southern Italy.

Between 2:39 a.m. and 2:53 a.m., the National Military Command Center gave formal authorization for the deployment of the two special operations force teams from Croatia and the U.S.

By 5:15 a.m., another assault was launched on a second U.S. facility on Benghazi which killed two former U.S. Navy SEALs identified as Tyrone Woods and Glen Doherty.

A C-17 aircraft stationed in Germany was ordered at 6:05 a.m. to be deployed to Tripoli to evacuate the personnel in the U.S. facilities under attack.

The first set of Americans was evacuated to Tripoli in the airplane at 7:40 a.m. with the help of the Libyan military, and the second group, including those killed, was flown to Tripoli at 10 a.m.

The C-17 which departed from Germany to Tripoli at 2:15 p.m. left the Libyan capital at 7:17 p.m. with consulate personnel and the bodies of those killed.

The U.S. special operations force team based in Croatia arrived at a staging base in Italy at 7:57 p.m. followed by a marine anti-terrorist team from Spain which arrived at 8: 56 p.m.

The U.S.-based special operations force team arrived at the staging base in Italy at 9:28 p.m.