President Trump now plans to blockade the Strait of Hormuz entirely. File Image / Pixabay

US President Donald Trump has threatened to detain vessels paying a toll to Iran to be allowed to pass through the Strait of Hormuz safely.

The US now plans to blockade the Strait of Hormuz entirely, preventing any ships from passing through, if Iran does not allow normal navigation in the region to resume, President Trump said in a social media post on Sunday.

"Effective immediately, the United States Navy, the finest in the world, will begin the process of blockading any and all ships trying to enter or leave the Strait of Hormuz," he said.

"I have also instructed our navy to seek and interdict every vessel in international waters that has paid a toll to Iran.

"No-one who pays a toll will have safe passage on the high seas."

Iran has effectively closed the Strait of Hormuz to commercial shipping since the start of March by attacking several vessels in the region and threatening to attack others seeking to pass through the key maritime chokepoint. More recently it has started to allow the passage of a few ships, passing through an Iranian-controlled route, reportedly in return for each ship paying a toll to Iran. 

In the short term, given the high commodity prices caused by the current conflict, some shipping companies may be willing to pay a toll in return for being allowed to continue their usual voyages. At question over the longer term is whether the US, Israel and other countries are willing to accept the imposition of a toll of this kind, and what they are prepared to do to prevent it if not.