Up to 275 US “military personnel” are being sent to Iraq to provide security for the US embassy in Baghdad and other personnel, the White House says.
The personnel will assist in the temporary relocation of some staff from the US embassy in Baghdad.
Fighters from the militant Sunni group ISIS have seized a number of Iraqi towns and cities in the past week.
Separately the US says it is willing to discuss with Iran what measures can halt the advance of the ISIS rebels.
However correspondents say that American officials have been quick to dismiss reports of military collaboration.
Speaking on Monday to Yahoo News, Secretary of State John Kerry said that Washington would “not rule out anything that would be constructive” while emphasising that any cooperation with Iran would be conducted on a “step-by-step” basis.
The UN says that Islamic State in Iraq and the Levant (ISIS) rebels have carried out hundreds of summary executions.
Human rights chief Navi Pillay said that systematic killings in the north of the country “almost certainly amounted to war crimes”.
Her remarks came as the militants, led by ISIS, were reported to have seized the strategic city of Tal Afar.
The rebels occupied several key cities last week, but some towns were retaken.
Security in Baghdad has been stepped up after the insurgents threatened to march on the capital, BBC informs.
