The officials said that there were indications that members of a militant faction calling itself Ansar al Sharia - which translates as Supporters of Islamic Law - may have been involved in organising the attack on the US Consulate in Libya's second-largest city.
They also said some reporting from the region suggested that members of al Qaeda's north Africa-based affiliate, known as al Qaeda in the Islamic Maghreb, may have been involved.
"It bears the hallmarks of an organised attack" and appeared to be preplanned, one US official said.
The officials asked for anonymity when discussing sensitive information. More specific details about the possible role of militant groups or cells in the attack were not immediately available.
One US official noted that, in the wake of the collapse of the government of the late Libyan leader Muammar Gaddafi last year, Libyan government arsenals were looted, making small arms and more sophisticated weapons available both to potential militants and black marketeers.
Some US officials cautioned against assuming that the Benghazi attack, or a similarly-timed violent protest at the US Embassy in Cairo, were deliberately organised to coincide with the anniversary of the September 11, 2001, attacks carried out by al Qaeda in Washington and New York.
US and European officials said that in contrast to the Benghazi attack, which some investigators say may have been calculated and organized, the attack on the US Embassy in Cairo appeared more likely to have been a spontaneous eruption by a mob.
Ambassador Christopher Stevens, Foreign Service Officer Sean Smith and two other Americans who have not yet been identified were killed when gunmen stormed the consulate and another US safe house in Benghazi on Tuesday.
A London think-tank run by a former Libyan militant leader suggested on Tuesday that not only was the Benghazi attack "well planned," but that it may have been retaliation for an American drone attack which killed a Libyan leader of al Qaeda's core command group earlier this year.
The Quilliam Foundation said that 24 hours before the Benghazi incident, al Qaeda leader, Ayman al-Zawahiri, distributed a video to militant websites in which he confirmed the death of his second in command, known as Abu Yahya al-Libi, and urged Libyans to avenge his killing.
Quilliam, whose president, Noman Benotman, once was a leader of an anti-Gaddafi militant faction known as the Libyan Islamic Fighting Group, said that according to its sources, up to 20 militants had prepared for a military assault.
Quilliam said the assault on the Benghazi Consulate took place in two waves. After the first wave, US officials arranged an evacuation of the Consulate by Libyan security forces. As the evacuation was taking place, a second wave of attacks was launched against US officials who had already been moved to a supposedly secure location, Quilliam said.
The Eurasia Group, a strategic consulting firm, said that it also believed that "the attack on the consulate was an orchestrated response by an organized Salafist (ultra-orthodox Muslim) group."
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So this has little to do with demonstrating against insults of Prophet Muhammad (PBUH) as depicted in a movie? And now, Washington officials are indicating that a terrorist faction is behind the killing of the US diplomat to avenge the death of one of their core command chiefs.
In civilized world and under various world conventions and treaties representative of a country is offered the best possible protection by the local government. This person represents the people of that country and not the government in power. In most case one may disagree with a policy of a government in power at that time but most people do not disagree with the people of that country.
There is something wrong with the Muslim world that conflict is always violent. Look at Mali, Sudan, Somalia, Nigeria, Pakistan, India, China, Chechnya (Russia), Yugoslavia, Palestine, Lebanon etc Muslim world needs its own Gandhi to teach them non violent conflict resolution. I suppose when one hears word Jihad umpteen times, one gets in to that state of mind and starts one whatever is easily available in front of that person. May be that is why that anger comes out either on minority or a sect with in the religion or on an external state or government that is perceived to have lot more than that of yours. E,g, against UK, USA, India, Russia, Serbia etc