The White House announced on Saturday that Joe Biden was returning to Washington from out of town “to consult with his national security team about events in the Middle East” amid heightened tension between Israel and Iran.

The US president had been due to spend the weekend in Delaware at his residence in Rehoboth Beach but early on Saturday afternoon set off at short notice to return to the White House.

This followed Biden saying on Friday that he expects an Iranian attack on Israel “sooner rather than later” and issued a last-ditch message to Tehran, saying: “Don’t.”

Earlier, John Kirby, the White House national security spokesperson, had warned that the threat of a significant Iranian attack on Israel remained “viable” despite Washington-led efforts, including calls to Tehran from the UK and Germany, to deter a serious escalation in the conflict in the Middle East.

On Saturday, Iran’s paramilitary Revolutionary Guard Corps in the strait of Hormuz, 50 nautical miles off the coast of the United Arab Emirates, seized an Israeli-affiliated container ship.

The ship’s operator, the Italian-Swiss group MSC, later confirmed that Iranian authorities had boarded it, rappelling from a helicopter. The White House condemned the seizure of the British-owned vessel.

National Security Council spokesperson Adrienne Watson said the US strongly condemned the seizure and urged Iran to release the ship and crew immediately.

“We will work with our partners to hold Iran to account for its actions,” she said, warning that “seizing a civilian vessel without provocation is a blatant violation of international law and an act of piracy.”.

Iran has threatened reprisals against Israel for a strike on the Iranian consulate in Syria on 1 April, in which seven members of the Revolutionary Guards including two generals were killed, sparking fears that an already volatile climate in the Middle East, with Israel and Hamas in Gaza at war, could quickly spiral further.

Lloyd Austin, the US defense secretary, spoke with Yoav Gallant, the Israeli defense minister, on Saturday to discuss urgent regional threats in the Middle East and “reiterated unwavering US support for Israel’s defense”, according to the Pentagon.

Gallant said the government is closely monitoring “a planned attack” by Iran and its proxies against Israel.

The US, along with its allies, have sent direct messages to Tehran to warn against further escalating the conflict.

The US national security adviser, Jake Sullivan, also spoke with his counterpart to reinforce Washington’s “ironclad commitment to the security of Israel”.

Although no information was given about whether a particular event or piece of intelligence prompted Biden to return suddenly to Washington, having determined earlier that leaving for a weekend in Delaware was all right, the news of the president’s actions gave a clear signal that the US believes the risk of some sort of Iranian attack on Israel has escalated.

Meanwhile, Lebanon’s Iran-backed Hezbollah group said it fired dozens of rockets at Israeli artillery positions on Friday, a bombardment it said was in response to Israeli strikes across the Israel-Lebanon border, the latest in near-daily exchanges of artillery.

Reuters, Agence France-Presse and the Associated Press contributed reporting

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