According to Fox News, citing sources, the increased hazard level will last for at least several days.
The report says that such a move "is considered a normal precaution given the current conditions on the ground."
According to the source, at the Balad Air Force Base, which came under fire at the end of last week, movement is allowed from 18:30 to 5:00 only in the framework of important tasks.
Earlier, the Pentagon confirmed a strike on the pro-Iranian militia in Syria by decree of US President Joe Biden.
The US said the strike was in response to recent attacks on US and coalition forces in Iraq.