U.S. President Donald Trump said Monday that any Iranian vessels approaching a U.S. blockade of Iranian ports would be "immediately eliminated,” escalating tensions with Tehran.

"Iran’s Navy is laying at the bottom of the sea, completely obliterated - 158 ships. What we have not hit are their small number of, what they call, 'fast attack ships,' because we did not consider them much of a threat,” Trump wrote on his social media platform Truth social.

"Warning: If any of these ships come anywhere close to our blockade, they will be immediately eliminated, using the same system of kill that we use against the drug dealers on boats at sea."

His warning came right after the U.S. Central Command (CENTCOM) began implementing a blockade of all maritime traffic entering and exiting Iranian ports.

NATO allies said on Monday ​they would not get involved in Trump's plan to blockade the Strait of Hormuz, proposing instead to intervene only once fighting ends, in a move likely ⁠to anger Trump and increase strains in the alliance.

The U.S. military ​later specified that the blockade, due to have started at 1400 GMT on Monday, ​would ⁠only apply to ships going to or from Iranian ports.

Since the start of the war on Feb. 28, Iran has largely blocked off the strait for all ships apart from its own. It has been seeking to make its control of the strait permanent and possibly collect levies from ships that use it.