Some personnel have been advised to leave the US military's Al Udeid Air Base in Qatar by Wednesday evening, three diplomats told Reuters, amid warnings from Washington that it could intervene to protect protesters in Iran.
The US embassy in Doha had no immediate comment and Qatar's ministry of foreign affairs did not immediately respond to a Reuters request for confirmation or comment.
Al Udeid is the Middle East's largest US base, housing around 10,000 troops.
"It's a posture change and not an ordered evacuation," one of the diplomats told Reuters. The diplomat said he was not aware that a specific reason had been given for the posture change.
A senior Iranian official told Reuters earlier that Tehran warned regional countries it would strike US military bases in case of an attack by Washington, after President Donald Trump threatened to intervene in Iran.
Last year, more than a week before the US launched air strikes on Iran, some personnel and families were moved off US bases in the Middle East. After the US attacks in June, Iran launched a missile attack on the base in Qatar.
