US President Donald Trump said the US will start escorting foreign vessels out of the Strait of Hormuz from Monday under a new "humanitarian" initiative.
In a post on Truth Social, Mr Trump said countries not involved in the Middle East conflict had asked Washington for help to free ships stranded in the strategic waterway.
Hours after the statement, the British Navy's maritime centre, based in Dubai, reported a vessel had been struck 78 nautical miles north of Fujairah in the Strait of Hormuz.
UKMTO said the ship was "hit by an unknown projectile" but that the crew was safe and the vessel was still operational.
The US operation could lead to an open conflict between Iran and American forces, but Mr Trump said neutral ships must be allowed safe passage.
“They are merely neutral and innocent bystanders. For the good of Iran, the Middle East and the United States, we have told these countries that we will guide their ships safely out of these restricted Waterways, so that they can freely and ably get on with their business,” he wrote.
Centcom said the effort, dubbed "Project Freedom", would include guided-missile destroyers, over 100 land and sea-based aircraft, drones and 15,000 service members.
“Our support for this defensive mission is essential to regional security and the global economy as we also maintain the naval blockade,” said Centcom chief Admiral Brad Cooper in a statement.
Mr Trump warned that any interference with the operation would be met with force.
“If, in any way, this humanitarian process is interfered with that interference will, unfortunately, have to be dealt with forcefully,” he said.
The operation will begin on Monday morning local time in the Middle East. Mr Trump said US officials were holding “very positive discussions” with Iran.
He said the ships would be able to resume normal operations, and that many vessels were low on food and essential supplies.
The comments come a day after he said he would study Iran's 14-point proposal, which calls for an end to the war in 30 days.
He earlier said he "can't imagine" that the proposal, which includes sanctions relief and an American withdrawal from the region, would be acceptable.
In a post on Truth Social, he said Iran had “not yet paid a big enough price for what they have done to humanity, and the world, over the last 47 years.”
