President Barack Obama has confirmed that U.S. Ambassador John Christopher (Chris) Stevens and three other State Department officials were killed when an angry mob stormed the U.S. Consulate in Libya.
According to reports, armed men attacked the consulate building in Benghazi late on September 11, setting it ablaze and burning it down.
Witnesses said the diplomatic building was ransacked and looted before being set on fire. They say it had also been badly damaged by homemade bombs and rocket-propelled grenades.
A statement by U.S. State Department spokeswoman Victoria Nuland said the United States condemned the attack "in the strongest terms" and was working with Libyan security forces to secure the compound.
Obama called the attack in Benghazi "outrageous and shocking," and vowed its perpetrators will face justice.
"I've also directed my administration to increase our security at diplomatic posts around the world," Obama said. "And make no mistake -- we will work with the Libyan government to bring to justice the killers who attacked our people."
He said the attack would not break the bond between Washington and Tripoli, adding that it was "especially tragic that Chris Stevens died in Benghazi because it is a city that he helped to save."
In a televised statement, Secretary of State Hillary Clinton denounced the consulate attack as "vicious" and said it "should shock the conscience of people of all faiths around the world."
She blamed "a savage but small group" for the killing of the U.S. diplomats but did not name the group.
"Today, many American are asking, indeed, I asked myself: 'How could this happen? How could this happen in a country we helped liberate, in a city we helped save from destruction?' This question reflects just how complicated and, at times, how confounding the world can be," Clinton said.
In Europe, NATO Secretary-General Anders Fogh Rasmussen said that "such violence can never be justified," and EU foreign-policy chief Catherine Ashton said it was "despicable."
The head of Libya's national assembly, Mohammed Magarief, said the authorities would bring the perpetrators to justice.
Local denizens interviewed near the destroyed U.S. Consulate building said the attack was the result of outrage over a low-budget film they say insults the Prophet Muhammad.
PHOTO GALLERY: Bloodshed in Benghazi
"The Libyans don't like [anybody] to say something bad about their prophet," one unnamed Benghazi resident told reporters. "Prophet Muhammad -- he is not Osama bin Laden. He is not anybody else. He is our prophet."
The film, titled 'Innocence of Muslims," reportedly was produced privately by a filmmaker in the United States.
"The Wall Street Journal" has reported that it was made by an Israeli-American named Sam Bacile who describes Islam as a "cancer" and depicts the Prophet Muhammad sleeping with women.
The Associated Press news agency quoted Bacile as saying that the film showed how Egypt's Coptic Christian minority is oppressed by the Muslim majority in Egypt.
Bacile has now gone into hiding, according to reports that cite a consultant on the film and Bacile himself.
Protests In Cairo
The attack in eastern Libya on September 11 came after an earlier protest by radical Islamists outside the U.S. Embassy in Cairo, the capital of neighboring Egypt.
The Cairo protesters were also angry about the film, which is being promoted by an anti-Muslim Egyptian Christian campaigner in the United States.
Excerpts of the film have been posted to YouTube and have been dubbed in Egyptian Arabic.
Earlier, the film was said to have been produced by Egyptian Coptic Christian expatriates in the United States.
U.S. Ambassador to Libya Chris Stevens took up his post in May.
Dozens scaled the walls of the embassy compound in Cairo. They tore down a U.S. flag, which was flying at half-mast to mark the anniversary of the September 11, 2001, terrorist attacks, and replaced it with a black Islamist banner.
One protester, Hossam Yousef Ismail, condemned criticism of the Prophet Muhammad, arguing that the right to free speech should not allow people to commit blasphemy against Islam.
"It is not right for a person to have the right to do just anything. That would be against a person's own interests. There is no such thing as unrestricted freedom. Even freedom has boundaries. Core religious beliefs should be respected by everyone in the world," he said.
"We are against this film we have heard about that insults the Prophet, peace be upon him, although I personally have not seen it. But we are trying to send a message to the whole world that we, as Muslims, have red lines, and that we have core beliefs. Whether or not the media try to make us deviate from our core beliefs, we will never do so."
Egyptian Prime Minister Hisham Kandil said the U.S. government should not be blamed for the insulting film.
He said the breach at the U.S. Embassy in Cairo was "regrettable and rejected by all Egyptian people and cannot be justified."
Egypt's powerful Muslim Brotherhood has called for nationwide protests on September 14 over the offending film.
Meanwhile, the U.S. Embassy criticized those who intentionally try to provoke Muslims by insulting their religious beliefs. In a statement, the embassy said it condemned "the continuing efforts by misguided individuals to hurt the religious feelings of Muslims -- as we condemn efforts to offend believers of all religions."
The statement added, "We firmly reject the actions by those who abuse the universal right of free speech to hurt the religious beliefs of others."
In Afghanistan, President Hamid Karzai condemned the film, saying its makers had done a "devilish act" and that insulting Islam was not allowed by freedom of speech.
Afghan authorities also briefly banned the YouTube website on September 12 to stop Afghans watching the satirical film.
The Taliban called on insurgents to "take revenge" on U.S. soldiers in Afghanistan.
And in Iran, the Foreign Ministry condemned the film as "repulsive" and said the U.S. government's "silence" encouraged such offenses to Islam. It made no mention of the attacks in Egypt and Libya.
With reporting by Reuters, AP, AFP, and dpa