Explosions were heard near the US embassy in Baghdad's heavily fortified Green Zone early on Friday and sirens calling on people to "duck and cover" were activated, according to social media videos from the scene verified by an informed source.
Embassy spokespeople did not immediately respond to requests for comment.
It was not immediately clear whether the embassy's air defence systems were activated or whether there was damage.
US forces at military bases in Iraq and Syria have faced more than 70 attacks since mid-October claimed by an umbrella organisation of Iraqi Shi'ite Muslim armed groups, though diplomatic missions have been spared.
No group immediately claimed responsibility for any attack on the U.S. embassy on Friday, which took place about 4 am.