Britain pulled its staff out of Iran on Friday amid mounting fears that the US is preparing imminent strikes.
The foreign office said its ability to support British nationals was now extremely limited, as rising tensions over a stalled nuclear deal threatened to throw the region back into all-out conflict.
Donald Trump has said he is “not happy” with how negotiations have gone with Iran, with more talks expected on Tehran’s nuclear programme.
Speaking to reporters on his way to Texas on Friday, Trump said: "I'm not happy with the fact that they're not willing to give us what we have to have. I'm not thrilled with that. We'll see what happens. We're talking later. We'll have some additional talks today."
Trump briefly laid out his case for a possible attack on Iran in his State of the Union speech on Tuesday, underlining that while he preferred a diplomatic solution, he would not allow Tehran to obtain a nuclear weapon.
It comes as an International Atomic Energy Agency report said Iran stored highly enriched uranium at underground sites, close to weapons grade.
Donald Trump’s stated deadline for Iran to make a deal is on course to expire as soon as Sunday, with insiders warning that negotiators remain far apart on key issues as Washington refuses to rule out an attack.
“Due to the ongoing security situation, we have taken the precautionary measure to temporarily withdraw UK staff from Iran,” Britain’s foreign ministry said, adding that the embassy would continue to operate remotely.
It also advised against all but essential travel to Israel and Palestine and said some diplomatic staff and their families had been moved from Tel Aviv to elsewhere in Israel.
Earlier on Friday, the United States allowed non-essential government staff and family members to leave Israel due to looming safety risks, while French citizens in Israel were told to identify bomb shelters.
Mike Huckabee, the US ambassador to Israel, told staff in an email that those wishing to leave “should do so TODAY”, according to The New York Times.
“There is no need to panic,” Mr Huckabee said. “But for those desiring to leave, it’s important to make plans to depart sooner rather than later.”
The US state department said secretary of state Marco Rubio would travel to Israel on Monday to discuss the burgeoning crisis and other regional priorities.
The French foreign ministry also advised nationals not to travel to Israel, Jerusalem or the West Bank in light of the worsening security situation in Iran. French citizens were told to be “vigilant, prudent and identify shelters”.
Separately, the Chinese embassy in Israel told its citizens to prepare themselves for an emergency, citing “rising security risks in the Middle East”, hours after telling nationals in Iran to evacuate as soon as possible.
While the Trump administration says it wants a diplomatic outcome to the crisis, it has refused to rule out limited strikes on Iran if a deal cannot be agreed.
Such an attack could trigger retaliation against Israel, which has already been hit by Iranian missiles in the past year.
Washington’s growing military presence in the Middle East was firmed up on Friday as the USS Gerald R Ford, the world’s largest warship, arrived off the coast of Israel, where the US has already reportedly sent a dozen F22 fighter jets.
A dozen warships were also operating in the northern Arabian Sea, including the USS Abraham Lincoln aircraft carrier.
Diplomats desperately worked to allay rising tensions with talks in Geneva earlier this week, but US officials told The Wall Street Journal that negotiations had failed to yield meaningful progress.
People familiar with the talks said Iran had objected to the idea of ending enrichment, dismantling its nuclear facilities, and imposing permanent restrictions on its programme – issues central to the dispute.
The UN nuclear watchdog separately issued a confidential report on Friday, urging Iran to let it inspect all its nuclear sites, which it said it had not seen since the US bombed them last year.
The International Atomic Energy Agency claimed that Iran had built a new enrichment plant at Isfahan and was stockpiling near-bomb-grade uranium there.
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