Britain has dramatically pulled family members of UK embassy staff out of Israel as the conflict with Iran intensifies.
They are understood to already have left the country amid fears over the deteriorating situation in the Middle East.
But thousands of ordinary Britons remain stranded, while Downing Street would not say whether or not they should attempt to flee.
Sir Keir Starmer will chair an emergency Cobra meeting on Wednesday afternoon amid reports President Donald Trump is considering entering the conflict between Israel and Iran.
A No 10 spokesman would only say they should "follow the advice of local authorities on staying close to shelter".
Amid confusion over the advice to British nationals, he added that there were spaces in buses and taxis heading for the border with Jordan but stopped short of suggesting Britons make the potentially dangerous journey.
While their families have left, embassy staff themselves are understood to have remained in Israel.
Over the weekend the Foreign Office warned Britons not to travel to Israel, but said there were no plans to repatriate citizens stuck there following the closure of Tel Aviv’s airport and the mass diversion and cancellation of flights.
On Tuesday Keir Starmer urged British nationals in Israel to register their presence there as countries step up efforts to bring back citizens.
Earlier this week the Independent highlighted the case of 15-year-old Bella Baker, stranded in a hotel in the northern Israeli port of Haifa, where on Monday 30 people were injured in a dawn missile attack on the city.
Foreign Office teams are understood to be working at the Jordanian border, to help people crossing by land from Israel, with both support and reassurance.
The decision to withdraw family members came as Israel's air campaign against Iran entered its sixth day, with jets striking the Iranian capital Tehran overnight.
US President Donald Trump is reported to be considering whether to deploy American forces in support of Israel.
Mr Trump has described Iranian supreme leader Ayatollah Ali Khamenei as an "easy target".
Earlier this week he left the G7 conference in Canada a day early to deal with what he called "big stuff", triggering speculation over the use of American forces.
Sir Keir had insisted Mr Trump was interested in de-escalation in the Middle East, saying "nothing" he had heard from the president suggested Washington was poised to get involved.
British Typhoon fighter jets have also been deployed to the region, which Defence Secretary John Healey said on Tuesday was "part of the moves to reinforce de-escalation in the region, to reinforce security in the region, and may also be used to help support our allies".