WASHINGTON, Sept 12 (Reuters) - The attack that killed the U.S. ambassador and three other American diplomats in Benghazi, Libya, may have been planned and organized in advance, U.S. government officials said on Wednesday.
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 organizing the attack on the U.S. 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 organized attack" and appeared to be preplanned, one U.S. 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 U.S. 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 U.S. officials cautioned against assuming that the Benghazi attack, or a similarly-timed violent protest at the U.S. Embassy in Cairo, were deliberately organized to coincide with the anniversary of the Sept. 11, 2001, attacks carried out by al Qaeda in Washington and New York.
U.S. 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 U.S. 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 U.S. 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, U.S. 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 U.S. 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."