The UK has raised the threat level for British forces in Iraq because of a heightened security risk from Iran, it is understood.
British personnel and their families in Saudi Arabia, Kuwait and Qatar are also said to be on an increased state of alert.
The move follows US claims of a heightened threat amid escalating tensions between Donald Trump’s administration and Tehran.
In a statement the Ministry of Defence said: “We keep the security of our deployed personnel and assets under constant review. There is a range of threats to UK and coalition forces in this part of the world: that is why we have a very robust range of force protection measures. The UK has long been clear about our concerns over Iran’s destabilising behaviour in the region.”
The move comes against a background of escalating tensions between Donald Trump’s administration and Tehran with the US stepping up its stringent sanctions regime against Iran over its nuclear programme.
Earlier today Iran’s foreign minister said sanctions imposed by the Trump administration are “unacceptable” but that his country is committed to an international nuclear deal that has steadily unraveled amid rising tensions.
On a visit to Tokyo, Mohammad Zarif defended Iran’s right to respond to the US pullout from the nuclear deal last year and the imposition of sanctions.
“We believe that escalation by the United States is unacceptable and uncalled for. We have exercised maximum restraints,” he said. In other comments carried on the semi-official Mehr news agency, Zarif was quoted as saying “a multilateral deal cannot be treated unilaterally”.