Protesters rankled by recent US air strikes on an Iran-backed Iraqi militia have supposedly broken into the US embassy compound in Baghdad.
US forces are said to have fired tear gas to disperse a crowd that breached the outer wall of the compound, which is in the heavily fortified Green Zone.
One of the guard towers was also apparently set alight.
About 25 fighters died on Sunday when the US bombarded bases related with Kataib Hezbollah in Iraq and Syria.
The US said it was fighting back for a rocket assault on an Iraqi army installation in Kirkuk on Friday that killed an American regular citizen contractual worker.
Iraqi Prime Minister Adel Abdul Mahdi said the air strikes had violated his country’s sovereignty and would force it to review its relations with the US.
Kataib Hezbollah’s leader, Abu Mahdi al-Muhandis, cautioned that the state army’s reaction “would be tough on the American forces in Iraq”.
Iran says the attacks is a “good example of terrorism”.