In a letter to Republican Sen. John McCain on Friday, Panetta specifically addressed the claim that the military could have dispatched armed unmanned aerial vehicles, AC-130 gunships or fighter jets to thwart the attack.
The Pentagon chief said these aircraft weren't near Benghazi and they were not an effective option.
Panetta insisted that the U.S. military did everything "they were in position" to do to respond to the attack and spared no effort save the four American lives.
The Associated Press obtained a copy of the letter.
