It was a Tweet but here’s another source.
The State Department on Wednesday ordered all non-critical government employees to leave Iraq and warned American citizens not to travel to the country over fears that growing tensions between the Trump administration and neighboring Iran could spark a conflict endangering them.
In a statement announcing the decision, officials cited a “high risk for violence and kidnapping” and said “normal visa services will be temporarily suspended” at the U.S. embassy in Baghdad and the U.S. consulate in Erbil. Some employees in Baghdad “will continue to provide consular services to U.S. citizens in Basrah,” the statement said.
https://www.nationalreview.com/news/american-civilians-ordered-to-leave-iraq-amid-iran-tensions/
Interesting. A "high risk for violence and kidnapping" points to domestic threats within Iraq, not a military threat from another country.