US President Joe Biden cut short a weekend trip to Delaware on Saturday for urgent consultations in Washington on the Middle East, the White House said, as tensions soar amid growing fears of an attack on Israel.

Iran has vowed retaliation after a presumed Israeli strike on April 1 leveled an Iranian diplomatic building in Damascus, killing seven members of the elite Revolutionary Guards including two generals.

A significant attack on Israel is expected in response, US officials have warned.

White House National Security Advisor Jake Sullivan said Saturday he spoke with Israel counterpart Tzachi Hanegbi to reiterate Washington's "ironclad" support.

"During the call, I reiterated the United States' ironclad commitment to the security of Israel," Sullivan said on X, adding the two discussed "events in the Middle East."

Tensions had already ratcheted up earlier in the day when Iran's Revolutionary Guards seized a container ship near the Strait of Hormuz that was "related to the Zionist regime," the term it uses for Israel, state media reported.

The ship's operator, the Italian-Swiss group MSC, later confirmed Iranian authorities had boarded it.

The White House condemned the seizure of the British-owned vessel.

"We call on Iran to release the vessel and its international crew immediately," said National Security Council spokeswoman Adrienne Watson.

"Seizing a civilian vessel without provocation is a blatant violation of international law, and an act of piracy by the Islamic Revolutionary Guards Corps."

Biden had said on Friday that he expected Iran to retaliate "sooner than later," and earlier this week had said Tehran was "threatening to launch a significant attack."

On Thursday the Pentagon said the top US commander for the Middle East had traveled to Israel for talks on security threats with the country's military officials.

The Strait of Hormuz connects the Gulf with the Indian Ocean and, according to the US Energy Information Administration, more than a fifth of annual global oil consumption passes through it each year.