Tensions rose sharply in the Strait of Hormuz on Friday after Iran's Revolutionary Guards Navy said four oil tankers caught fire and exploded while trying to use routes it had not authorised. The claims came alongside separate reports of a tanker being hit by an unidentified projectile and Iranian claims of shooting down an American drone and destroying an unmanned naval vessel. Iranian state media carried the claims, but they could not be independently verified.

In its latest statement, the Islamic Revolutionary Guard Corps Navy said a fourth tanker, carrying more than 2 million barrels of crude oil, had struck a naval mine, causing a powerful explosion and a fire. An earlier statement had reported another tanker carrying 2 million barrels of crude hitting a naval mine. The force linked the incidents to vessels navigating routes it had not approved.

The Strait of Hormuz connects the Gulf to the Gulf of Oman and carries around one-fifth of the world's oil supplies, so any disruption to tanker movement there has immediate implications for international energy markets and shipping. The latest reports arrive amid sustained tensions in the waterway following US and Israeli strikes on Iran at the end of February.

UK agency reports a tanker hit by a projectile

Separately, the United Kingdom Maritime Trade Operations agency said it had received reports of an incident involving a crude oil tanker in the strait. According to a verified source cited by the agency, a tanker was struck by an unidentified projectile while completing its outbound transit through the waterway.

In an earlier update, the agency said a vessel had been hit on its port side by an unknown projectile about 40 nautical miles, or 74 kilometres, south of Iran's Lavan Island, setting off a fire on board. The agency said all crew members were safe and there had been no reported environmental impact. Lavan Island lies off Iran's southern coast in the Gulf. It was not immediately clear whether the vessel reported by the British agency was among the four tankers mentioned by the Revolutionary Guards Navy.

Iran's drone claims rejected by US military

Iranian state media also reported that Iranian forces had shot down and captured an American MQM-170 drone over Qeshm Island, near the Strait of Hormuz. There was no immediate response from the US military to that specific claim. In another announcement, Iran said it had destroyed an unmanned US naval vessel in the eastern part of the strait.

The US military's Central Command rejected the naval vessel claim, saying all American unmanned surface vessels deployed in the Middle East had been accounted for, including a squadron of advanced sea drones on patrol in the Strait of Hormuz. With the tanker claims unverified, the projectile report confirmed only as an incident by the British agency, and the drone and vessel claims contested, the full picture of Friday's events in the strait remained unclear, even as the reports underlined how volatile one of the world's most important energy chokepoints has become.