Hundreds of more US Marines are being sent to Iraq to reinforce security at the American embassy in Baghdad.
It follows days of violent protests over US airstrikes on an Iranian-backed militia in which 25 people were killed.
One of the air strikes hit the headquarters of paramilitary group Kata’ib Hezbollah - blamed for attacking American soldiers during the Iraq war.
Washington said the strikes were retaliatory and blamed the militias for dozens of recent attacks on bases housing coalition personnel. A US contractor was killed in one of the attacks.
During protests in the Iraqi capital, militia supporters attacked the entrance to the US embassy and set alight the perimeter.
However, according to US officials, the perimeter remained intact and there were no plans for evacuation.
A quick reaction force, of 100 Marines, was deployed and rushed in by helicopter from Kuwait.
President Donald Trump thanked US forces for their swift response and gave reassurances there would be no repeat of 2012, when terrorists killed the US ambassador to Libya during a siege on the American embassy in Benghazi.
The US is sending 750 airborne troops to Baghdad - 14,000 extra soldiers have already been sent from the US to the Middle East in the past six months.
President Trump tweeted to say Iran would pay a heavy price if any US lives were lost.
Cover Image: US Marines prepare for deployment from North Carolina to secure US embassy in Baghdad.