US Defense Secretary Lloyd Austin made an unannounced trip to Iraq on Tuesday, in a visit that an official said was aimed at showing that Washington was committed to keeping its military presence there nearly 20 years after the US-led invasion toppled Saddam Hussein. "What (Iraqi's) will hear from him is commitment to retaining our force presence, but it's not just about the military instrument. The United States is broadly interested in a strategic partnership with the government of Iraq," the senior US defense official, speaking on the condition of anonymity, told reporters. Austin was the last commanding general of US forces in Iraq after the 2003 invasion.