A deadly assault on a U.S. consulate in Libya was a spontaneous reaction to an anti-Muslim video, U.S. Ambassador to the United Nations Susan Rice said even as Libya’s President insisted the attackers spent months preparing and carefully choosing their date, the anniversary of the Sept. 11 terrorist attacks.

Unnerved by the rapidly escalating raid on Tuesday that claimed the life of the U.S. Ambassador to Libya and three other Americans, the Obama administration last week launched an investigation into whether terrorist groups had exploited outrage over an anti-Muslim video to trigger an attack long in the works.

But Ambassador Susan Rice said on Sunday that evidence gathered so far shows no indication of a premeditated or coordinated strike. She said the attack in Benghazi, powered by mortars and rocket-propelled grenades, appeared to be a copycat of demonstrations that had erupted hours earlier outside the U.S. Embassy in Cairo, spurred by film excerpts posted on YouTube.

“It seems to have been hijacked, let us say, by some individual clusters of extremists who came with heavier weapons,” Ms Rice said, adding that such weaponry is easy to come by in post-revolutionary Libya.

Whether those extremists had ties to al-Qaeda or other terrorist groups has yet to be determined, Ms Rice said, noting that the FBI is yet to complete its investigation.

Ms Rice’s depiction of the chain of events contrasted with one offered by Libya’s Interim President Mohammed el-Megarif, who said Sunday there was no doubt the perpetrators had predetermined the date of the attack.

“It was planned, definitely. It was planned by foreigners, by people who entered the country a few months ago,” el-Megarif said. “And they were planning this criminal act since their arrival.”

Brushing aside el-Megarif’s assessment, Ms Rice said it wouldn’t be the first time that Western works critical of Islam have triggered spontaneous unrest throughout the Middle East. She pointed to Salman Rushdie’s novel “The Satanic Verses” and cartoons of the Prophet Muhammad published by a Danish newspaper in 2006.

But Rep. Mike Rogers, chairman of the House Intelligence Committee, said it was premature to rule out a premeditated attack. A former FBI agent, Mr Rogers said there were too many coincidences to conclude the Benghazi attack hadn’t been planned in advance.

“There’s other information, classified information we have that just makes you stop for a minute and pause,” Mr Rogers said, without elaborating.

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