Speaking at Camp Pendleton in California, US, Hagel said the newly deployed personnel will help the US continue its ongoing aid by providing more in-depth assessments of the humanitarian situation.
"This is not a combat boots on the ground kind of operation. We’re not going back into Iraq in any of the same combat mission dimensions that we once were in Iraq."
An unnamed US defence official said the additional soldiers are Marines and Special Operations forces who will assess the feasibility of rescuing thousands of Yazidis trapped on Mount Sinjar.
The soldiers will reportedly work with the US State Department and representatives from the US Agency for International Development to coordinate plans with international partners and non-government organisations on how to evacuate the Yazidi refugees.
Another US defence official was quoted by Associated Press as saying that the mission for the additional troops could last less than a week.
In June, the Pentagon sent 300 military advisers to help the Iraqi Government combat ongoing violence from Islamic State (IS) militants.
To date, US military aircraft have delivered more than 85,000 meals and nearly 20,000 gallons of fresh drinking water to the Yazidis, who fled their homes in the wake of an IS offensive.
In addition, over the past five days US F/A-18, F-15E and MQ-1 Predators have bombed several IS positions to stop their advances in northern Iraq.
The UK Royal Air Force is also air-dropping food, water, tents and solar-powered lights that also serve as mobile telephone chargers.
Meanwhile, Germany has raised the possibility of sending military aid to the Iraqi Government.
German Foreign Minister Frank-Walter Steinmeier was quoted by Frankfurter Allgemeine Zeitung as saying: "Humanitarian aid for everyone that needs protection is a matter of course … but we must look [at] whether we can and must do more."