Sen. John McCain criticized President Barack Obama for his lack of involvement in the developing civil war in Syria.
"I think it was a planned, premeditated attack," Senate Armed Services Chairman Carl Levin (D-Mich.) said. He added he did not know the specific group responsible for the assault on the complex.
McCain expressed a similar view.
"People don't go to demonstrate and carry RPGs and automatic weapons," he said, adding that the facts suggest "this was not a 'mob' action [or] a group of protesters."
"Whenever something like this happens, there is obviously ... a failure. Whether that failure was of great significance or nonsignificance or it was one of those things that probably couldn't have been prevented," McCain said. "I'm not ready to indict our intelligence community until we get more facts"
However, Collins said she had serious concerns about the security at the consulate in Benghazi, particularly in the aftermath of other incidents over the summer involving the Americans and the British.
"My overwhelming concern is that I don't understand why the consulate was not better guarded, given the attacks that were aimed at the British ambassador in June, the bomb that exploded outside the consulate - also in June," Collins said. "The threat environment was such that to leave the defense to Libyan nationals just doesn't make sense to me."
In the immediate aftermath of the attack on the consulate, Obama ordered additional resources to provide security to diplomatic facilities in the region.
Vice President Joe Biden waits to conduct a mock swearing-in ceremony with Sen. Brian Schatz, D-Hawaii, in the Capitol's Old Senate Chamber, December 2, 2014. Schatz was sworn in to serve the remainder of his term since he was appointed to the seat after Sen. Daniel Inouye, D-Hawaii, passed away.