The Foreign Office has issued a travel alert for 19 countries amid fears that conflict in Lebanon could escalate into a wider regional war.
British tourists have been warned to remain vigilant in hotspots including Egypt, Tunisia and Morocco.
Other countries on the list include Jordan, Qatar, the United Arab Emirates and Saudi Arabia.
The warning reads: “Ongoing hostilities between Israel and Lebanon could escalate quickly and pose risks for the wider region. Monitor this travel advice and other media as the situation is changing fast.”
Meanwhile, the UK Government has urged an estimated 5,000 British citizens in Lebanon to leave immediately.
The Prime Minister’s official spokesman said Sir Keir Starmer has been “very, very clear” that British nationals “should leave now, particularly whilst commercial flights are still available”.
The warning follows the killing of Hezbollah leader Hassan Nasrallah by Israel in a rocket strike in Beirut on Friday.
Hezbollah responded by saying it is ready to fight should Israel launch a ground offensive, with fears mounting that the escalating hostilities could result in a full-scale regional war.
A US official told the BBC’s US partner CBS that an invasion into the country could begin as soon as Monday.
It came after Israeli defence minister Yoav Gallant hinted that a ground invasion of Lebanon could be imminent as he urged troops to use “all the abilities we have” to return displaced residents north of the border.
But Hezbollah’s acting leader promised the group will fight on following Nasrallah’s death.
Naim Kassem said: “We are ready for a ground invasion, and we will emerge victorious.”
Over 1,000 people have been killed in Lebanon in the past two weeks, nearly a quarter of them women and children, according to the Health Ministry.
The Israeli military on Monday evening declared the areas around the communities of Metula, Misgav Am, and Kfar Giladi in northern Israel near the border with Lebanon as a closed military zone and said entry to the areas was prohibited.
It said the decision was taken following a situational assessment.
The UK and the US have called on Israel and Lebanon to seek a diplomatic resolution to the violence to allow tens of thousands of displaced Israelis and Lebanese to return to their homes along the border.
US Secretary of State Anthony Blinken told reporters that Washington “will continue to work with our partners in the region and around the world to advance a diplomatic resolution”.