The US embassy said staff had been told not to travel outside the greater Jerusalem, Tel Aviv or Beersheba areas "out of an abundance of caution".

Iran has vowed to retaliate, blaming Israel for a strike on its consulate in Syria 11 days ago, killing 13 people.

Two US officials have told the BBC's US partner CBS News that an attack could come as soon as Friday.

One unnamed official said the attack could include more than 100 drones, dozens of cruise missiles and perhaps ballistic missiles as well and will be aimed at military targets in Israel.

Israel has not claimed responsibility for the consulate attack on 1 April but is widely considered to have been behind it.

Iran backs Hamas, the armed Palestinian group fighting Israel in Gaza, as well as various proxy groups throughout the region, including some - such as Hezbollah in Lebanon - that frequently carry out strikes against the Israelis.

Those killed in the consulate attack included a senior commander of Iran's elite Quds Force in Syria and Lebanon, as well as other military figures.

The attack came at a time of continuing diplomatic efforts to prevent the war in Gaza spreading across the region.

Speaking on Wednesday, US President Joe Biden warned Iran was threatening to launch a "significant attack" and vowed to offer "ironclad" support to Israel.

Israeli Prime Minister Benjamin Netanyahu said his government was ready to meet any security challenge, warning that Israel would harm any country that caused it harm.

"We are prepared to meet all of the security needs of the State of Israel, both defensively and offensively," he said.

The commander responsible for US operations in the Middle East, Erik Kurilla, has travelled to Israel for talks with officials on security threats.

The Pentagon said the visit had been scheduled previously but had been brought forward "due to recent developments".