The U.S. ambassador to Libya, J. Christopher Stevens, and three other Americans were killed in an assault on the American consulate in Benghazi on Tuesday by protesters angry about an online film considered offensive to Islam. Stevens is the first U.S. ambassador to be killed in an attack since 1979. The mob that stormed the consulate with guns and rocket-propelled grenades -- burning, ransacking and badly damaging it -- were allegedly furious about a 14-minute YouTube video ridiculing Mohammed produced by an Israeli-American real estate developer living in California, according the Wall Street Journal. The U.S. Embassy in Egypt was also attacked Tuesday in response to the film. President Barack Obama called the attack "outrageous" and said, "Chris was a courageous and exemplary representative of the United States." Secretary of State Hillary Clinton identified a second victim as Sean Smith, a Foreign Service information management officer who was a 10-year veteran of the State Department, a husband and a father of two. The other two victims have not been named.