Non-essential US embassy staff and their dependants in Baghdad are to be evacuated from Iraq due to heightened security risks, US government sources have said.
Officials did not say exactly what prompted the removal, however, in recent days talks over Iran's nuclear programme appear to have stalled.
A US state department official told the BBC on Wednesday: "We are constantly assessing the appropriate personnel posture at all our embassies.
"Based on our latest analysis, we decided to reduce the footprint of our mission in Iraq."
This move comes after weeks of talks between the US and Iran - President Trump has hoped to strike a deal to stop Tehran developing a nuclear weapon.
Trump said on Wednesday he was growing less confident that Iran would stop enriching uranium.
Earlier this week he also held a 40-minute phone call – said to be "tense" - with Israel's prime minister, who has long argued for a military rather than diplomatic approach.
Asked on Wednesday evening about the decision to evacuate staff from multiple parts of the Middle East, Trump said: "Well, they are being moved out because it could be a dangerous place, and we'll see what happens."
He added: "But they are been – and we've given notice to move out, and we'll see what happens."
With the nuclear talks at a critical moment, it isn't yet clear how much the US announcement is about signalling as opposed to genuine concern.
But Iranian Defence Minister Aziz Nasirzadeh said his country would retaliate against US bases in the region if talks failed and Trump ordered military strikes against the Islamic Republic.
Reuters news agency reports that US Defence Secretary Pete Hegseth also approved the voluntary departure of families of American military personnel from countries across the Middle East, including Kuwait and Bahrain.
Testifying in front of a congressional panel on Wednesday, the Pentagon said he believed there are "plenty of indications" that Iran is "moving their way towards something that would look a lot like a nuclear weapon".
Iran says its uranium enrichment programme is for civilian energy generation and that it is not trying to build an atomic bomb.
Also on Wednesday, the UK's Maritime Trade Operations organisation - part of the Royal Navy - issued a warning saying that increased military tensions in the Middle East could affect shipping.
The price of oil initially increased more than 4% when news of the US evacuation broke, in anticipation of regional insecurity potentially leading to supply problems.
Around 2,500 US troops are based in Iraq, according to the defence department.
Additional reporting by Tom Bateman in Washington