The United States ambassador to Libya, J. Christopher Stevens, was killed in a rocket attack on the American Consulate in the city of Benghazi on Tuesday, a contractor working at the mission said Wednesday after seeing Stevens' body.

Three American security staff were also killed, said the contractor, who asked not to be named for security reasons.

The deaths came as protesters attacked U.S. diplomatic compounds in Libya and Egypt on Tuesday, angry about an online film considered offensive to Islam.

The United States has not confirmed the deaths.

Stevens was the American envoy to the Libyan rebel movement that overthrew dictator Moammar Gadhafi last year, based in the rebel capital of Benghazi.

The last time an American ambassador was killed by terrorists was in 1979, when the envoy to Afghanistan, Adolph Dubs, was kidnapped and killed during an attempt to rescue him, according to State Department records.