File photo: US official said they have increased security and defensive measures at Iraqi bases which host coalition troops. AFP
"I'm here to reaffirm the US-Iraq strategic partnership as we move toward a more secure, stable and sovereign Iraq," Austin tweeted as he landed in Baghdad.
The defense secretary is expected to meet top officials during his visit to Iraq, which is home to about 2,000 of American troops. NATO has also several hundred troops there.
Iraq has endured nearly two decades of turmoil since a US-led coalition invaded Iraq in 2003.
The IS group seized roughly one third of Iraq and declared a "caliphate" in 2014, before its defeat more than three years later.
Despite their defeat, IS militants and their sleeper cells are still launching attacks in the country, as well as in neighboring Syria. IS has killed and wounded dozens of Iraqi troops over the past months.
The United States has been urging countries around the world to repatriate their citizens from al-Hol camp in northeast Syria, which holds tens of thousands of mostly women and children linked to IS. The vast majority of them are Iraqis and Syrians.
Iraq has repatriated more than 500 women and children from al-Hol over the past weeks.
Iraq has been caught for years in a delicate balancing act between its two main allies, the United States and Iran, and Baghdad only recently arrived at a fragile compromise government after a year of political stalemate.
Months earlier, Iraqi Prime Minister Mohammed Shia al-Sudani defended the open-ended presence of US and other foreign troops in his country, in an interview to The Wall Street Journal, published on January 15.
In February, Iran's top diplomat Hossein Amir-Abdollahian held talks with neighbouring ally Iraq to ease regional tensions and discuss security along their shared border.
On several occasions, Sudani expressed his country's desire to have good relations with both the United States and Iran.
"We strive for that," he added. "I don't see this as an impossible matter, to see Iraq have a good relationship with Iran and the US."