Displaced Iraqis from the Yazidi community cross the Iraqi-Syrian border along the Fishkhabur bridge over the Tigris River at the Fishkhabur crossing, in northern Iraq, on August 11, 2014.

Defense Secretary Chuck Hagel announced the deployment in remarks to Marines at Camp Pendleton, California.

"This is not a combat boots on the ground kind of operation," Hagel said.

Another defense official, speaking on condition of anonymity to provide additional details on the sensitive mission, said the extra troops are Marines and special operations forces whose mission is to assess the situation in the Sinjar area and to develop additional humanitarian assistance options beyond current U.S. efforts there.

The 130 troops arrived Tuesday in the city of Irbil, well east of Sinjar. They are to work with representatives of the State Department and the U.S. Agency for International Development to prevent potential acts of genocide by the Islamic militants who forced them from their villages, the defense official said.

The move shows the Obama administration is weighing the impact and implications of several days of targeted airstrikes on the Islamic State fighters and how that has affected U.S.-backed Kurdish forces opposing them in northern Iraq.

President Barack Obama has said repeatedly he will not send ground combat forces back into Iraq.

One immediate dilemma is the fate of thousands of displaced civilians in the Sinjar area who have been provided with food and water delivered by U.S. cargo planes in recent days. Washington also is considering how to increase its military assistance to the Kurds, whose militia is outgunned by the militants.

The 130 are in addition to 90 U.S. military advisers already in Baghdad and 160 in a pair of operations centers — one in Irbil and one in Baghdad — working with Iraqi security forces. They are in addition to about 455 U.S. security forces and 100 military personnel working in the Office of Security Cooperation in the U.S. Embassy in Baghdad.