Reports say the U.S. ambassador to Libya and three other embassy staff were killed after a mob stormed the American consulate in the eastern city of Benghazi late Tuesday.

The death occurred when demonstrators angered over an amateur American-made film that insults Islam's Prophet Muhammad shot at and set fire to the U.S. consulate in Benghazi.

Earlier, U.S. Secretary of State Hillary Clinton had confirmed that only a single U.S. official was killed in the Benghazi attack, which she condemned “in the strongest terms.”

Clinton said some have sought to justify “this vicious behavior” as a response to inflammatory material posted on the Internet. She said the U.S. deplores any intentional effort to denigrate the religious beliefs of others, but rejected any “justification for violent acts of this kind.”

In Egypt, protesters scaled the fortified walls of the U.S. embassy in Cairo, tore up an American flag and replaced it with an Islamic banner. The demonstrators there – mainly ultraconservative Islamists – continued their protest action through the early hours of Wednesday.

The mobs were sparked by outrage over the film that U.S. media said was produced by Israeli-American Sam Bacile, who describes Islam as a “cancer,” and financed by expatriate members of Egypt's Coptic Christian minority group. Clips of the film in English and Arabic have recently been posted on YouTube.

The Associated Press reported that Bacile – a California real estate developer – went into hiding Tuesday.

The video is being promoted by controversial Florida-based Christian Pastor Terry Jones, who said Tuesday the film is not designed to attack Muslims but to show the “destructive ideology of Islam.” Jones inspired deadly riots in Afghanistan in 2010 and 2011 by threatening to set fire to copies of the Quran and then burning one in his church.

The protests coincide with the 11th anniversary of the September 11th terrorist attacks in the United States.