Cyprus and Türkiye were included in the list as the Foreign Office issued new travel advisories for countries in the Gulf region.
The updates came as the US launched a 12th straight night of attacks on Iran.
The two countries signed a Memorandum of Understanding last month to halt military operations and reopen the Strait of Hormuz, and reach an agreement to end the war within the next 60 days.
But three weeks after it was signed, US President Donald Trump announced a ceasefire following Iranian attacks on ships in Hormuz and US retaliatory strikes.
New notices from the Foreign, Commonwealth and Development Office (FCDO) provide “an update on regional tensions following the recent Iranian strike and retaliatory attacks.”
Countries covered by the updated guidelines also include Bahrain, Jordan, Kuwait, Yemen, Oman, Israel, Qatar, Saudi Arabia, Syria, Iraq and Palestine, with the notable absence of the UAE.
The advice notes that the situation in the Middle East “remains unpredictable” and urges travelers to sign up for FCDO email alerts, monitor the latest media information, follow instructions from local authorities and keep departure plans “under review” while ensuring travel documents are up to date.
The government also announced that British staff had temporarily withdrawn from Iran and the British embassy was working remotely.