The US military did not intervene quickly during the attack on America's consulate in Libya because military leaders did not have adequate intelligence information and felt they should not put their forces at risk, defence secretary Leon Panetta said.
In his most extensive comments to date on the unfolding controversy surrounding the attack in Benghazi, Mr Panetta said US forces were on heightened alert because of the anniversary of the September 11, 2001 attacks and prepared to respond.
But, he said, the attack happened over a few hours and was over before the US had the chance to know what was really happening.
"(The) basic principle is that you don't deploy forces into harm's way without knowing what's going on; without having some real-time information about what's taking place," Mr Panetta told Pentagon reporters.
"And as a result of not having that kind of information, the commander who was on the ground in that area, General Ham, General Dempsey and I felt very strongly that we could not put forces at risk in that situation."
Mr Panetta was referring to Gen Carter Ham, the head of US Africa Command, and Gen Martin Dempsey, chairman of the Joint Chiefs of Staff.
In a letter to President Barack Obama yesterday, House of Representatives speaker John Boehner questioned whether the White House considered military options during or immediately after the attack, and what the president knew about the security threats in the country.
He said the national debate over the incident showed that Americans were concerned and frustrated about the administration's response.
"Can you explain what options were presented to you or your staff, and why it appears assets were not allowed to be pre-positioned, let alone utilised? If these reports are accurate, the artificial constraint on the range of options at your disposal would be deeply troubling," Mr Boehner, a Republican, wrote.
US ambassador Chris Stevens and three other Americans were killed in the attack, which has become a heated campaign issue less than two weeks before the election.
Republicans have criticised the Obama administration's failure to acknowledge more quickly that intelligence suggested very early on that it was a planned terrorist attack rather than spontaneous violence erupting out of protests over an anti-Muslim film.
House and Senate Republicans as well as Republican presidential candidate Mitt Romney have criticised President Obama and administration officials over the response to the attack and whether officials failed to provide enough security at the consulate.
And there have been ongoing questions about whether there should have been additional military forces sent to the consulate immediately after it became clear that the Americans were under attack.
As the events were unfolding, the Pentagon began to move special operations forces from Europe to Sigonella Naval Air Station in Sicily.
US aircraft routinely fly in and out of Sigonella and there are also fighter jets based in Aviano, Italy.
But while the US 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.
Also, the Pentagon would not send forces or aircraft into Libya - a sovereign country - without a request from the State Department and the knowledge or consent of the host nation.
During his news conference Mr Panetta lamented the "Monday morning quarterbacking" that has been going on about how the US handled the attack. And Gen Dempsey, sitting alongside Mr Panetta, bristled at questions about what the military did or did not do in the aftermath.
Noting that there are reviews already going on, Gen Dempsey added, "It's not helpful, in my view, to provide partial answers. I can tell you, however, sitting here today, that I feel confident that our forces were alert and responsive to what was a very fluid situation."
Military officials have noted that there had been no specific intelligence pointing to a possible attack in Libya, and that there were protests and other unrest in various locations around the Middle East and Africa.
Asked whether the military was on alert in that area because of 9/11, Gen Dempsey added, "Yeah, and let me point out, it was - it was 9/11 everywhere in the world."
The Senate Intelligence Committee has announced it will hold a closed hearing on November 15 into the circumstances surrounding the terrorist attack, including the intelligence and security situation there, and additional hearings will follow.