Reports of Iranian gunboats opening fire on a tanker in strait, after Tehran said it is closing the waterway until the US lifts the blockade of its ports.

Iran says it has closed the Strait of Hormuz again, calling the decision a response to a continued blockade of its ports by the United States.

The Iranian military on Saturday said control of the strategic waterway, through which 20 percent of the global oil flows, has “returned to its previous state”, with reports saying Iranian gunboats fired at a merchant vessel as it attempted to ‌cross.

The closure of the strait came hours after it was reopened, with more than a dozen commercial ships passing through the waterway, after a US-mediated 10-day ceasefire deal was reached between Israel and Lebanon.

The Islamic Revolutionary Guard Corps (IRGC) on Saturday said in a statement, cited by the Iranian media, that the ongoing US blockade of Iranian ports represented “acts of piracy and maritime theft”, adding that the control over Hormuz is “under the strict management and control of the armed forces”.

“Until the US restores full freedom of navigation for vessels travelling from Iran to their destinations and back, the status of the Strait of Hormuz will remain tightly controlled and in its previous condition,” it said.

By 10:30 GMT on Saturday, no fewer than eight oil and gas tankers had crossed the strait, but at least as many ships appeared to have turned back, having begun to exit the Gulf, the AFP news agency reported.

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-Israel war on Iran was “very close”.

Trump had celebrated the reopening of the strait on Friday, but warned the US attacks would resume until Iran agreed to a deal, which included its nuclear programme.

“Maybe I won’t extend it,” Trump told reporters on board Air Force One about the temporary ceasefire agreement in place. “So you’ll have a blockade, and unfortunately we’ll have to start dropping bombs again.”

Asked whether a potential deal could be made in this short timeframe, Trump said: “I think it’s going to happen.”

But Iran says no date has been agreed for another round of peace talks, accusing the US of “betraying” diplomacy in all negotiations.

The conflicting and changing reports about the strait and how much freedom ships have to transit through it have deterred many vessels from crossing, according to John-Paul Rodrigue, a maritime shipping specialist at Texas A&M University.

“Ships have been attempting transit since the announcement, but it looks like many of them are heading back because the situation is unclear,” Rodrigue told Al Jazeera. “There is contradictory information being issued by all parties.”

Reporting from Tehran, Al Jazeera’s Tohid Asadi said “uncertainty is the name of the game” as far as the Strait of Hormuz is concerned.

“Iran is looking for a comprehensive end to the war across the region, security assurances, sanctions relief, the unfreezing of frozen assets, regional relations – and on top of all of that – the nuclear dossier and Iran’s stockpile of highly enriched uranium,” he said.

“But right now, uncertainty is the name of the game. The fragile situation makes it hard to talk about the possibility of successful negotiations down the road.”