CAMP PENDLETON, Calif. » Another 130 U.S. troops arrived in Iraq on Tuesday on what the Pentagon described as a temporary mission to assess the scope of the humanitarian crisis facing thousands of displaced Iraqi civilians trapped on Sinjar Mountain and evaluate options for getting them out to safety.

Defense Secretary Chuck Hagel announced the deployment in remarks to Marines at this Southern California base on the final stop of a week-long, around-the-world trip that also took him to India, Germany and Australia.

"This is not a combat boots on the ground kind of operation," Hagel said. "We’re not going back into Iraq in any of the same combat mission dimensions that we once were in in Iraq," he added, referring to the eight-year war that cost more than 4,400 U.S. lives and soured the American public on military involvement in Iraq.

Another defense official, speaking on condition of anonymity to provide additional details on the sensitive mission, said the extra troops were Marines and special operations forces whose mission was to assess the situation in the Sinjar area and to develop additional humanitarian assistance options beyond current U.S. efforts there. Still another official said the mission for the 130 troops could last less than one week.

That official also said that while the troops were not being sent in to execute some type of rescue mission of the Yazidis on the mountain, they would assess the feasibility of a rescue or what one might look like. The also would assist in the ongoing effort to evaluate the use of airstrikes as part of the mission to protect the Yazidis from attacks by the Islamic State militants.

Hagel referred to the 130 as "assessors."

The additional troops arrived Tuesday in the city of Irbil, well east of Sinjar. They were to work with representatives of the State Department and the U.S. Agency for International Development to coordinate plans with international partners and non-government organizations to help the trapped Yazidi civilians on Sinjar Mountain.

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

The 130 were 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 were 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.

U.S. officials said that while Obama put caps on the number of troops deployed to Iraq, these latest forces were being sent under the authorization for humanitarian assistance and therefore did not exceed the limits.

Burns reported from Washington.