CAIRO (MCT) — The attack on a U.S. diplomatic post in eastern Libya that killed the U.S. ambassador and three other Americans was carried out by a small group of militants who arrived late at night, unleashed a fusillade from AK-47 rifles and rocket-propelled grenades, then torched and ransacked the building, according to witnesses and U.S. officials.

U.S. officials said the two-hour assault on the U.S. Consulate in Benghazi appeared planned and “complex,” rather than a spontaneous outbreak of mob violence in reaction to an online video, purportedly produced in the United States, that mocks the Muslim Prophet Muhammad. The video had prompted protesters to scale the U.S. Embassy walls in Cairo earlier Tuesday and tear down an American flag.