The United States will send 200 more troops and a number of Apache helicopters to Iraq to assist in the fight against Isis.
Defence Secretary Ash Carter said the new forces will mostly be used to advise Iraqi forces closer to the front lines.
The announcement marks the first major increase in US forces for nearly a year, and was made during a push to retake the key city of Mosul from Isis control.
President Barack Obama pledged to increase the authorised troop level in Iraq from 3,870 to 4,087.
Most of the additional 217 troops will likely be Army special forces, who have been used to advise and assist the Iraqi army.
They are often embedded with Iraqi brigades and battalions, putting them at greater risk from mortar and rocket fire.
The Apache helicopters are considered a significant asset for any attack on Mosul, Iraq's second-largest city.
US military officials have made it clear winning back Mosul is critical to the fight against Isis.
However, any assault on the city is likely to be challenging, as the militants have dug in and are likely to have peppered the landscape with roadside bombs.
Additional reporting by Associated Press
