The United States on Monday promised to lead a "collective response" against Iran in retaliation for a deadly attack on an Israeli-linked tanker.
The United States and Israel have both said that their intelligence concluded that an Iranian drone on Thursday attacked the MT Mercer Street, managed by prominent Israeli billionaire Eyal Ofer, as it sailed off Oman.
A British security guard and a Romanian crew member were killed in what analysts said bore all the hallmarks of the "shadow war" between enemies Iran and Israel.
US Secretary of State Antony Blinken called the MT Mercer Street incident "a direct threat to freedom of navigation and commerce."
"We are in very close contact, in coordination, with the United Kingdom, Israel, Romania and other countries. And there will be a collective response," Blinken told reporters, the second straight day he has threatened retaliation.
Britain summoned the Iranian ambassador and demanded that vessels navigate freely in the oil-rich region.
"I think that Iran should face up to the consequences of what they've done," British Prime Minister Boris Johnson told reporters, condemning the "unacceptable and outrageous attack" on the ship.