America, caught by surprise by the ferocious September 11 attack against the US consulate in Libya that killed the US ambassador and three other countrymen, is bracing itself for more potential violence in parts of the Muslim world.
Fears are growing that another attack will come after Friday's weekly prayers - traditionally a time of protest in the Middle East and North Africa.
Angry demonstrations over an anti-Islam video have already occurred in Egypt and Yemen and officials believe well-armed Libyan extremists hijacked a similar protest in Benghazi, where several Libyan security guards were also killed.
The US put all of its diplomatic missions overseas on high alert and secretary of state Hillary Clinton delivered an explicit denunciation of the video as the administration sought to pre-empt further turmoil at its embassies and consulates.
"The United States government had absolutely nothing to do with this video," she said, before a meeting with the foreign minister of Morocco at the US State Department. "We absolutely reject its content and message. To us, to me personally, this video is disgusting and reprehensible. It appears to have a deeply cynical purpose - to denigrate a great religion and to provoke rage."
US officials said they suspect that the attack at the Benghazi consulate, which had also been the target of an unsuccessful attack in June, may have been only partially related to the film.
They also stressed there had been no advance warning or intelligence to suggest a threat in Libya that would warrant boosting security, even on the 11th anniversary of the terror attacks of September 11 2001.
The intelligence leading up to the attacks will be examined to "see if there was any way of forecasting this violence", as in any violent incident, House of Representatives Intelligence Committee member Adam Schiff said. But he said the focus now "has to be on finding out who is responsible and bringing them to justice".
President Barack Obama, speaking a campaign event in Golden, Colorado, also vowed that the perpetrators would be punished. "I want people around the world to hear me," he said. "To all those who would do us harm - no act of terror will go unpunished. I will not dim the light of the values that we proudly present to the rest of the world. No act of violence shakes the resolve of the United States of America."
As of Thursday night, there was no intelligence indicating that what happened in Benghazi was planned, according to two US officials. Intelligence chiefs believe it is more likely that the attack was "opportunistic or spontaneous", with militants taking advantage of the demonstration to launch the assault. There is also no evidence that the attack was tied to 9/11, one of the officials said. But the Libyan-based militant group Ansar al Sharia is the leading suspect for carrying out the violence, possibly with help from al Qaida's main African-based offshoot, Al Qaida in the Islamic Maghreb.
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