Tehran, Iran - Iran's military declared the Strait of Hormuz closed again on Saturday, prompting ships to abandon attempts to transit the waterway and President Donald Trump to warn Tehran against trying to "blackmail" the US.

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

This prompted elation in global markets and sent oil prices plunging, with Trump insisting that a US naval blockade of Iranian ports would continue until a deal to end the wider Middle East war was concluded. Tehran threatened to shut the strait once more.

Late on Saturday morning, Iran's central military command said that, in response to the US blockade, "control of the Strait of Hormuz has returned to its previous status" and "is under strict management and control of the armed forces."

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Trump had previously said the two sides were "very close" to striking a deal, but following Iran's announcement on Saturday, he insisted Tehran "can't blackmail us," even as he maintained communications were ongoing.

"We'll be talking about Iran later. We have very good conversations going on," he added, accusing Tehran of getting "a little cute" with its recent moves.

Iran's top national security body, meanwhile, said that during a visit by the military chief of mediator Pakistan that concluded Saturday, "new proposals have been put forward by the Americans, which the Islamic Republic of Iran is currently reviewing and has not yet responded to."

It went on to say, however, that Iran's negotiating delegation would not offer "even the slightest compromise, retreat or leniency" in talks with Washington.

There are just four days remaining before the end of the two-week ceasefire in the US and Israel's war on Iran, launched by Washington and its ally on February 28.