In its latest statement reported on Iranian state media on Friday, the IRGC Navy said a fourth vessel, a tanker carrying more than 2 million barrels of crude oil, had hit a mine, suffered a powerful explosion and was burning.
An IRGC Navy statement had said earlier that one of the tankers, which was also carrying 2 million barrels of crude oil, had hit a naval mine.
Reuters was unable to immediately verify the statement.
Separately, the United Kingdom Maritime Trade Operations agency said it had received a report of an incident in the Strait of Hormuz.
A verified source told the agency a crude oil tanker was struck by an unknown projectile while completing an outbound transit of the waterway.
Earlier, UKMTO said it had received a report a vessel was hit by an unknown projectile on its port side about 40 nautical miles (74 km) south of Iran's Lavan Island, causing a fire on board.
The crew were reported safe and there was no reported environmental impact, it said.
Lavan Island lies in the Gulf, off Iran's southern coast. It was not immediately clear whether the vessels cited by UKMTO were among the four tankers referred to by the IRGC Navy.
Tensions have persisted in the Strait of Hormuz, a strategic waterway through which around one-fifth of global oil supplies pass, since the US-Israeli strikes on Iran at the end of February.
State media said Iranian forces also downed and captured an MQM-170 US drone over Iran's Qeshm island near the Strait of Hormuz.
There was no immediate reaction from the US military and Reuters could not independently verify the report.
Iran also said it had destroyed an unmanned US vessel in the eastern Strait of Hormuz.
But the US military's Central Command denied this and said in a statement on X: "All U.S. military unmanned surface vessels in the Middle East are accounted for, including a squadron of advanced sea drones on patrol in the Strait of Hormuz."
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