Mohammad Hannon/AP Photo

The latest intelligence assessment of the attack on the U.S. diplomatic mission in Benghazi indicates there was little if any pre-planning for it and that it was in part an opportunistic response to the protests at the U.S. Embassy in Cairo.

Ambassador Chris Stevens and three other Americans were killed in the attack, which has become a political hot potato in the presidential campaign with questions over when the Obama administration called the attack an act of terrorism.

"Right now, there isn't any intelligence that the attackers pre-planned their assault days or weeks in advance," said a U.S. intelligence official. "The bulk of available information supports the early assessment that the attackers launched their assault opportunistically after they learned about the violence at the U.S. Embassy in Cairo." But the official added that "no one is ruling out that some of the attackers may have aspired to attack the U.S. in Benghazi."

Republican lawmakers have seized on U.S. Ambassador to the U.N. Susan Rice's comments on Sunday talk shows days on September 16 attributing the deadly Benghazi attack to spontaneous protests against an anti-Muslim film made in the U.S. that had been posted on the Internet. As more information emerged they pointed to the use of mortars and RPG's in the attack as indicating it was not a spontaneous protest as the Obama administration had claimed, but an act of terrorism.

Rice's comments were based on talking points she had been provided by the intelligence community. The intelligence official said those talking points were written for members of Congress and senior U.S. officials so they "could say something preliminary about the attacks." The official said they reflected "the early indications of extremist involvement in a direct assault" and that "it wasn't until after the points were used in public that people reconciled contradictory information and assessed there probably wasn't a protest around the time of the attack."

On September 28 a spokesman for the Director of National Intelligence's office issued a press release revising the initial assessment that the attack on "began spontaneously following protests earlier that day at our embassy in Cairo." The spokesman said new information indicated it "was a deliberate and organized terrorist attack carried out by extremists."

The DNI said it remained unclear if "if any group or person exercised overall command and control of the attack, and if extremist group leaders directed their members to participate. However, we do assess that some of those involved were linked to groups affiliated with, or sympathetic to al-Qaeda."

The current assessment is the latest shift in a narrative that has become politicized on Capitol Hill and the presidential campaign. At a hearing before the House Oversight House and Government Reform Committee last week, State Department officials said there had been no protests outside the consulate compound at least an hour before the attack.

The official said the assessment evolved once again as "it was clear from the outset that a group of people gathered that evening." He added, "A key question early on was whether extremists took over a crowd or if the guys who showed up were all militants. It took time-until that next week-to sort through varied and sometimes conflicting accounts to understand the group's overall composition."