The US government has said it will stand with the people of Israel after Iran revealed plans to launch a retaliatory attack.
The retaliation by Iran follows a deadly air strike on its Damascus consulate. The White House has repeatedly warned Tehran against carrying out an attack on Israel.
Tehran had vowed to avenge the April 1 strike – which killed 16 people, including two Iranian generals, and has been widely blamed on Israel.
Iran’s Revolutionary Guards seized a container ship “related” to Israel in the Strait of Hormuz on Saturday.
The ship’s operator, the Italian-Swiss group MSC, said it was working with the relevant authorities to ensure the wellbeing of the 25 crew onboard.
Both Israel and the United States denounced the seizure as piracy, with Israel also demanding that the Guards be declared a “terrorist organisation” by the European Union.
In Washington, National Security Council spokeswoman Adrienne Watson called on Iran “to release the vessel and its international crew immediately”.
“Seizing a civilian vessel without provocation is a blatant violation of international law, and an act of piracy”, she said.