The US President Barack Obama has authorised deployment of an additional 350 soldiers to Iraq to help protect the Baghdad Embassy compound and its support facilities.
Pentagon press secretary rear admiral John Kirby said in a statement: "This builds upon previous embassy security deployments announced on June 15 and June 30 and will bring the total forces responsible for augmenting diplomatic security in Iraq up to approximately 820.
"The additional joint forces will come from within the US Central Command area of operations and will include a headquarters element, medical personnel, associated helicopters, and an air liaison team.
"In all, 405 US military personnel will be sent to Baghdad to provide a more robust and sustainable security presence to help the Department of State continue their critical mission."
White House press secretary Josh Earnest said: "This action was taken at the recommendation of the Department of Defense after an extensive interagency review and is part of the President's commitment to protect our personnel and facilities in Iraq as we continue to support the Government of Iraq in its fight against the Islamic State of Iraq and the Levant (ISIL).
"These additional forces will not serve in a combat role.
"The request he approved today will allow some previously deployed military personnel to depart Iraq, while at the same time providing a more robust, sustainable security force for our personnel and facilities in Baghdad."
The deployment announcement comes on the same day the ISIL released a video showing the beheading of the second US journalist, Steven Sotloff, who was kidnapped in Syria in August 2013.
The group had threatened to execute Sotloff if the US continued airstrikes on IS targets in Iraq in a video last month, which showed the beheading of journalist James Foley in an almost identical fashion.
Since 8 August, the US military has conducted a total of 124 airstrikes on ISIL terrorists across Iraq.
The US, along with its allies, including Australia, France, Germany and the UK, is also arming the Iraqi Government and Kurdish forces fighting insurgents in the country.