Tensions have flared in the region after US president Donald Trump ordered the strike on Qasem Soleimani near Baghdad airport on Friday (3 January).
Foreign minister Dominic Raab said the UK understood why the US took action against Soleimani and urged Iran to ease tensions via diplomatic channels.
It comes after Trump and the Iranian republic shared a series of aggressive exchanges over the weekend, with Tehran vowing to avenge Soleimani’s death. The US has sent an additional 3,000 troops to the region, while Trump has said the US is ready to strike 52 Iranian targets.
The FCO issued fresh travel bulletins on Saturday morning (4 January) advising against all travel to Iraq, except essential travel to the Kurdistan region, and all but essential travel to Iran.
Any Britons in either Iran are urged to "consider carefully" their need to remain. "If your continued presence is not essential, you should consider leaving," said the FCO.
"There is a risk that British nationals, and a significantly higher risk that British-Iranian dual nationals, could be arbitrarily detained or arrested in Iran," the FCO added. "The criminal justice process followed in such cases falls below international standards.
"Iran does not recognise dual nationality. If you are a dual British-Iranian national and are detained in Iran, the FCO’s ability to provide consular support is extremely limited."
Those in areas of Iraq where the FCO has advised against all travel are urged to "consider leaving by commercial means".
Elsewhere, the FCO has also updated its travel advice for those travelling to other Gulf nations and neighbouring countries and territories.
This includes Egypt, Oman, Qatar, Kuwait, Bahrain, the United Arab Emirates, Saudi Arabia, Turkey, Yemen, Syria, Palestine, Israel, Afghanistan and Lebanon.
"British nationals in the region should remain vigilant and keep up to date with the latest developments, including via the media and this travel advice," the FCO added.
