American soldiers inside the embassy have fired tear gas, stun grenades and warning shots at hundreds of fighters who broke down the compound gate and set fires within the complex on Tuesady
The ambassador was on leave at the time of the attack and embassy staff had already been evacuated before the US marine guard became besieged at the compound
Trump has vowed to hold Tehran accountable for the embassy attack, which is in retaliation for US air strikes on the Iran-backed Kataeb Hezbollah on Sunday night
Those USAF strikes were themselves in retaliation for last week's killing of an American contractor in Kirkuk
'Iran killed an American contractor, wounding many. We strongly responded, and always will.' Trump tweeted on Tuesday morning. 'Now Iran is orchestrating an attack on the U.S. Embassy in Iraq. They will be held fully responsible. In addition, we expect Iraq to use its forces to protect the Embassy, and so notified!'