An American staff member of the US consulate in the Libyan city of Benghazi has died following fierce clashes at the compound. Several others were wounded.
Armed militants attacked the offices but were eventually forced to retreat by gunfire from Libyan security forces.
Itis thought the incident was provoked by a US-produced film that is said to be insulting to the prophet Mohammad.
Although the building was burnt to the ground and items of furniture looted, no one was inside at the time.
The protest happened as hundreds in neighbouring Egypt continued their own demonstration outside the US embassy in Cairo.
The film that has caused so much anger among Muslims is said to have been produced by some Egyptian Copt expatriates. A trailer of it has appeared on YouTube in Arabic.
Earlier protesters had scaled the walls of the embassy and torn down and burnt the American flag.
Some have called on President Mohamed Morsi, Egypt’s first civilian president and an Islamist to intervene.