The Government has strengthened its warnings over travelling to Iraq and Iran, following the killing of a top Iranian general in a US air strike.
The Foreign Office has urged British nationals to not to travel to Iraq, except for essential travel to the Kurdistan region, and only essential travel to Iran.
It also called on Britons in Iraq to consider leaving the country by commercial means.
The warning came as thousands of mourners in Baghdad chanted "death to America", while they took part in the funeral procession of General Qassem Soleimani.
Gen Soleimani, who was responsible for Iran's military campaigns abroad as leader of the elite Quds Force, was killed by a US drone strike at Baghdad airport on Friday.
The US said he was killed for "actively developing plans" to kill Americans, while Iran warned of "severe revenge".
Foreign Secretary Dominic Raab, who urged "all parties to de-escalate", said the updated advice for Britons was issued due to "heightened tensions in the region" and would be kept under review.
"The first job of any government is to keep British people safe," he said.
The Foreign Office also urged Britons in the region to "remain vigilant and monitor the media carefully".
US President Donald Trump said the killing of Gen Soleimani was "to stop a war, not to start one", as US officials announced 3,000 extra troops were being sent to the Middle East as a precaution.
Following the attack, the UK began reviewing its "force protection" in the region.
Around 400 British Army personnel are deployed in Iraq across three bases in non-combat roles, while there are also six Royal Navy ships in the Gulf.
Outgoing Labour leader Jeremy Corbyn has written to the Prime Minister, calling for an urgent meeting of the Privy council to discuss whether the "assassination" had heightened the terror risk to the UK.
"The UK Government should urge restraint on the part of both Iran and the US, and stand up to the belligerent actions and rhetoric coming from the United States," Mr Corbyn said.
"All countries in the region and beyond should seek to ratchet down the tensions to avoid deepening conflict, which can only bring further misery to the region, 17 years on from the disastrous invasion of Iraq."
Boris Johnson, who has been celebrating the New Year in the Caribbean, has not yet commented on the general's killing.
Cover Image: A picture of General Qasem Soleimani is seen above a road in Iranian capital, Tehran (Picture: PA).