US President Barack Obama on Wednesday strongly condemned the killing of the US ambassador to Libya and three other embassy staff as an "outrageous attack" and ordered increased security at US diplomatic posts worldwide.

"I have directed my administration to provide all necessary resources to support the security of our personnel in Libya, and to increase security at our diplomatic posts around the globe," Obama said in a statement after the US diplomats were killed in Benghazi.


Film by Israel-American which allegedly sparked the mob violence

"While the United States rejects efforts to denigrate the religious beliefs of others, we must all unequivocally oppose the kind of senseless violence that took the lives of these public servants," he said.

US ambassador to Libya Christopher Stevens and three other embassy staff were killed in a rocket attack on their car, a Libyan official said, as they were rushed from a consular building stormed by militants denouncing a US-made film insulting the Prophet Mohammad. Conflicting reports suggested the diplomats were killed by crowds storming the embassy.

Gunmen had attacked and burned the US consulate in the eastern city of Benghazi, a center of last year's uprising against Muammar Gaddafi, late on Tuesday evening, killing one US consular official. The building was evacuated.

The Libyan official said the ambassador was being driven from the consulate building to a safer location when gunmen opened fire.

"The American ambassador and three staff members were killed when gunmen fired rockets at them," the official in Benghazi told Reuters.

US Secretary of State Hillary Clinton on Wednesday condemned the attack as the work of a "small and savage group" but said US-Libyan ties would not suffer.

"I ask myself, how could this happen? How could this happen in a country we helped liberate, in a city we helped save from destruction?" Clinton said. "This question reflects just how complicated and, at times, how confounding the world can be."

"But we must be clear-eyed even in our grief. This was an attack by a small and savage group, not the people or government of Libya," she added in a brief appearance.

Clinton said a free and stable Libya was in US interests and that ties between the two countries would not be a "casualty" of the attack.

Libyan deputy prime minister Mustafa Abu Shagour condemned the killing of the US diplomats as a cowardly act.

The consular official had died after clashes between Libyan security forces and Islamist militants around the consulate building. Looters raided the empty compound and some onlookers took pictures after calm returned.

In neighboring Egypt, demonstrators had torn down an American flag and burned it during the protest. Some tried to raise a black flag with the words "There is no God but God, and Mohammad is his messenger", a Reuters witness said.

Mob violence possibly sparked by Israeli-American film

US pastor Terry Jones, who had inflamed anger in the Muslim world in 2010 with plans to burn the Koran, said he had promoted "Innocence of Muslims", which US media said was produced by an Israeli-American property developer; but clips of another film called "Mohammad, Prophet of Muslims", had been circulating for weeks before the protest.

That film portrayed Mohammad as a fool, a philanderer and a religious fake. In one clip posted on YouTube Mohammad was shown in a sexual act with a woman.

Jones, a pastor in Florida whose latest stunt fell on the anniversary of the Sept. 11, 2001, attacks on the World Trade Center and the Pentagon, triggered riots in Afghanistan in 2010 with his threat to burn the Koran.

Many Muslims consider any depiction of the Prophet offensive and any depiction of him can cause outbursts of anger in the Islamic world and among Muslims in Europe.

Libya's interim government has struggled to impose its authority on a myriad of armed groups that have refused to lay down their weapons and often take the law into their own hands.

It was clearly overwhelmed by Tuesday night's attack on the consulate that preceded the assault on the ambassador.

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