President Donald Trump said the United States would start helping to free ships stranded in the Gulf by the US-Israeli war on Iran from Monday, as a tanker reported being hit by unknown projectiles in the Strait of Hormuz.

Trump gave few details of the plan to aid ships and their crews that have been "locked up" in the vital waterway and are running low on food and other supplies.

"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," Trump said in a post on his Truth Social site on Sunday.

Hundreds of ships and as many as 20,000 seafarers have been unable to transit the strait during the conflict, the International Maritime Organization says.

US Central Command said it would support the effort with 15,000 military personnel, more than 100 land and sea-based aircraft, along with warships and drones.

"Our support for this defensive mission is essential to regional security and the global economy…