Thousands of Iranians have marched on the streets of Tehran to protest against US and UK policy in Iraq.
A police cordon prevented serious damage to the embassy building
Demonstrators also hurled petrol bombs at the British embassy but no serious damage was reported.
The protesters held placards and chanted slogans denouncing coalition troops for fighting in the Iraqi cities of Najaf and Karbala, sacred to Shias.
The marchers were summoned by a call from Iran's Shia clergy - a frequent critic of the Iraq occupation.
The BBC's Jim Muir in Tehran says several hundred protesters initially gathered at the British embassy.
Their ranks were swelled by up to 3,000 more, some of whom then broke away from the main demonstration.
Petrol bombs and bricks were hurled at the building by protesters who were kept at a distance by a cordon of riot police.
Similar protests also took place outside the British embassy on Sunday.
Wednesday's march drew to a climax in Tehran's enormous Inghelab (Revolution) square, where protesters burned American, British and Israeli flags.
Iran's leaders have been calling for demonstrations in three cities - Tehran, Mashhad and the holy city of Qom.
"Muslims cannot tolerate the insolent attacks by US soldiers against the holy places and these crimes can only be condemned in the eyes of the Islamic world, the Shias and the Iranian people," the country's supreme leader, Ayatollah Ali Khamenei, said.
US troops have been blockading the Iraqi city of Najaf, where they have met stiff resistance from Shia militiamen loyal to radical cleric Moqtada Sadr.
Sporadic skirmishes between the two parties have caused minor damage to the dome of the shrine of Imam Ali, an important figure in the Shia faith.
Though critical of the Americans, Iran's clergy has stopped short of backing Mr Sadr.