The United States has restricted travel for its diplomats in Israel amid reports of an imminent attack from Iran.
The US embassy has advised staff to avoid travelling outside the greater Jerusalem, Tel Aviv or Beersheba areas "out of an abundance of caution".
Israel is on high alert after Iran's Supreme Leader, Ayatollah Ali Khamenei, vowed to take revenge following its bombing of Iran's consulate in Damascus on April 1, which killed several military officials.
Israel warned this week that it would respond to an attack with strikes against Iran. The US has moved to offer assurance to its ally.
The head of US Central Command, General Michael "Erik" Kurilla, flew into Israel on Thursday to co-ordinate against the Iranian threat, after President Joe Biden promised "ironclad" support despite rising tensions between Washington and Tel Aviv over the war in Gaza.
British Prime Minister Rishi Sunak said the UK would also back Israel.
"The threats from Iran are completely unacceptable and we, like the Americans, fully support Israel's right to defend itself," he said.
"We have already highlighted Iran as a significant risk to regional security and we have always said that we will support Israel's ability to defend itself and we are taking action ourselves to make sure we can protect the UK against threats from Iran."
It has been reported that foreign diplomats in Israel have been advised to stock up on essential items in anticipation of an attack by Iran.
Iranian officials quoted by news outlet Amwaj predicted a "limited but precise strike", and suggested a target in the Golan Heights, occupied by Israel but recognised as Syrian territory, would carry "less risk".
Asked about the travel restrictions on Thursday, state department spokesperson Matthew Miller said he would not disclose the "specific assessments" behind them, but added: "Clearly we are monitoring the threat environment in the Middle East and specifically in Israel."
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The UK Foreign Office has also updated its travel advice for Israel to state that the country's government has raised the "possibility of an attack on Israeli territory from Iran, and that such an attack could trigger wider escalation".
