Security forces responded with a volley of fire, it's not currently clear if or how many demonstrators were injured.
Update - Additional angles appear to show that this was tear gas and flash bangs.
Earlier in the night Iraqi's in Baghdad filmed security forces rolling tanks near the Green Zone.
The US has the world biggest embassy in the zone and it's described as "overlooking the Tigris River". It's not clear the number of US troops in the area but due to the embassy they are some there.
The US still has a few thousand military advisers so the US might be in command of some of the elements.