"Suffice it to say that the commander-in-chief would not make a decision to put our men and women in harm's way without getting some necessary assurances," Xinhua quoted spokesperson Josh Earnest as saying.
President Barack Obama ordered all American troops out of Iraq after failing to obtain legal immunity for those to be left behind, but he announced last week that as many as 300 US military advisors would be sent back as part of measures to help Baghdad counter the lightening advances by fighters from the Islamic State in Iraq and the Levant, a splinter group of Al Qaeda also known as ISIL.
"We can confirm that Iraq has provided acceptable assurances on the issue of protections for these personnel, via the exchange of diplomatic note," Earnest said. "We believe these protections are adequate for the short-term assessment and advisor mission our troops will be performing."
Pentagon spokesperson John Kirby said with the protection offered, the military "will be able to start establishing the first few assessment teams".
The ISIL has seized two big cities -- Mosul and Tikrit -- and other towns in northern and western Iraq in the past two weeks, and took control of two main border crossings with Syria over the weekend.
Obama has held off airstrikes on the militants despite a request by Iraqi Prime Minister Nuri al-Maliki, calling instead for the establishment of an inclusive government in Baghdad.
US Secretary of State John Kerry visited Baghdad Monday and had talks with Maliki and other leaders, as insurgents continue to expand their control across the country.