US President Donald Trump has said the military operation to guide stranded merchant ships through the Strait of Hormuz will be paused just two days after he announced it.

Trump declared on Sunday that "Project Freedom" would begin the next morning in an attempt to unblock the crucial waterway which Tehran has effectively closed since the start of the US-Israel war with Iran.

Iran's threats to ships using the strait - through which some 20% of the world's oil and gas flows - has led to large increases in the oil price and fears for the global economy.

But 50 hours later the president posted that the mission was being put on hold "for a short period of time".

His decision came on the same day his defence secretary had declared the US was "leading with strength, clarity and purpose for the benefit of the entire world".