Iran's military declared the Strait of Hormuz closed again on Saturday, its military command said, hours after reopening it, The Caspian Post reports, citing AFP.

The toing and froing over the strait cast doubt on US President Donald Trump's optimism the day before, that a peace deal to end the US-Israeli war with Iran was "very close".

Tehran had on Friday declared the strait, which usually carries a fifth of the world's oil and liquefied natural gas, open on Friday after a ceasefire was agreed in Lebanon to halt Israel's war with Hezbollah.

That prompted elation in global markets and sent oil prices plunging, but with Trump insisting that a US naval blockade of Iranian ports would continue until a deal was concluded, Tehran threatened to shutter the strait once more.

Then, late on Saturday morning, citing a statement from military central command, Iranian state TV reported that "control of the Strait of Hormuz has returned to its previous status" and "is under strict management and control of the armed forces", blaming the continued US blockade.

The announcement came as maritime tracking sites showed several ships making a dash through the narrow waterway, hugging close to Iranian territorial waters as instructed by Tehran and, for some, broadcasting their identity as Indian or Chinese in an apparent attempt to show their neutrality.

The same sites showed that late on Friday, a number of ships began heading for the strait before suddenly turning back amid the uncertainty.

By 0900 GMT on Saturday, several ships had fully transited the strait in both directions, but at least two tankers headed eastwards from the Gulf towards India after loading in UAE ports appeared to have turned around and aborted their journeys.