The U.S. sent 129 additional military personnel to Iraq to help develop an evacuation plan for tens of thousands of Iraqis stranded on a mountain under threat from Islamic extremists in northern Iraq. The new deployment raises the level of American military personnel in the country to 935, including 250 military advisors already in place, as well as an additional 100 assigned to the U.S. Embassy and the airport in Baghdad. At least 100 aircraft and more than half a dozen ships are also available to assist in the ongoing crisis.

The mission so far is focused on humanitarian operations and the protection of U.S. assets and personnel. But there have also been more than a dozen targeted air strikes against Islamic State of Iraq and the Levant fighters bearing down on the Kurdish capital of Iraq—including a strike from a remotely piloted aircraft on an ISIL armed truck west of the village of Sinjar on Wednesday afternoon. Late Wednesday, Pentagon spokesman Rear Adm. John Kirby said a team of less than 20 U.S. advisors returned from a 24-hour assessment of Mount Sinjar having decided an evacuation mission is now "far less likely," citing the success of the air support mission and "the efforts of the Peshmerga and the ability of thousands of Yazidis to evacuate from the mountain each night over the last several days."

Meanwhile, even with the hundreds of troops on the ground and fighter pilots in the air, the Obama administration insists there isn’t a combat mission in Iraq.

"We don't believe that involves U.S. troops re-entering a combat role in Iraq," Deputy National Security Adviser Ben Rhodes said Wednesday. "It involves frankly a very difficult logistical challenge of moving folks who are in danger on that mountain into a safer position.”

“This is not a combat boots-on-the-ground operation,” Defense Secretary Chuck Hagel told Marines at Camp Pendleton, Calif., on Tuesday. “We're not going back into Iraq in any of the same combat mission dimensions that we once were in, in Iraq…[and] this is not any extension of any role other for the United States other than to find ways to assist and help advise the Iraqi security forces, which we have been doing.”

Rhodes called the situation at Sinjar Mountain urgent and unsustainable and said the president is expected to make a decision on possible expanded military options in a matter of days—including sending ground troops to help the refugees, many of them Yadizi minorities targeted by ISIL. "There needs to be a lasting solution that gets that population to a safe space where they can receive more permanent assistance,” Rhodes said.

U.S. aircraft late Wednesday carried out their seventh drop of water to thousands of Iraqis stranded on Mount Sinjar. But with every additional troop and aircraft operating on the ground and in the skies near the northern Kurdish stronghold of Irbil, the risks of violence coming to international troops in Iraq grows more imminent.

(Read More: America Has No Strategy to Stop ISIL)

British pilots on Wednesday completed their fifth drop of supplies, including water and shelters, to Sinjar refugees. And France announced on Wednesday it would begin arming the Kurds after the European Union failed to arrive at a consensus on how to arm Kurdish peshmerga troops near Irbil. The Australians, too, will soon be joining in the humanitarian effort in Iraq, Hagel said after signing a pact Tuesday to keep U.S. troops in Australia until the year 2040.

A top Pentagon official told reporters Monday that the effect of U.S. airstrikes is unlikely to stop the momentum of the fast-advancing Sunni militants intent on creating a new Islamic state in Iraq, Syria and beyond.

“This fiction that Americans are not going to be in a combat role is just that,” retired Air Force Lt. Col. Rick Francona told CNN.

The new batch of troops consists of Marines and special operations forces from within the U.S. Central Command region, a defense official said. Members of Congress questioned whether the addition of these troops was leading to mission creep and asked President Barack Obama to more clearly outline his plans and goals in Iraq.

“I support providing humanitarian relief to Iraqi civilians and measures to protect American personnel, but I am concerned about the timeline and scope of our renewed military efforts in Iraq,” said Sen. Tim Kaine, chairman of the Senate Foreign Relations Subcommittee on Near Eastern, South and Central Asian Affairs, in a statement Tuesday. “No one doubts the barbarity of IS [or ISIL] and [the] threat it poses to our partners and I will always support the president if he takes action to protect American servicemembers and diplomats. But the mission and objectives of any military action must be made clear to Congress, the American people, and our men and women in uniform.”