Sudanese security forces fired tear gas to disperse around 10 000 protesters who marched on the US embassy in the capital on Friday after attacking the British and German missions, an AFP correspondent said.
Clashes erupted after a large number of security forces blocked off roads leading to the embassy as stone-throwing demonstrators protesting over a film deemed offensive to Islam tried to approach.
"God is greatest" and "Do not touch the Prophet" were among slogans chanted by the demonstrators.
An estimated 5000 protesters earlier stormed the embassies of Britain and Germany, which was torched and badly damaged.
Police fired tear gas as several protesters scaled the roof of the German embassy and others attacked its facade, tearing down the flag to replace it with a black Islamist one, the AFP reporter said.