"The master of a container ship reported that the vessel was approached by one IRGC gunboat... that then fired upon the vessel, which has caused heavy damage to the bridge. No fires or environmental impact reported," the United Kingdom Maritime Trade Operations centre said.

It added that the incident took place 15 nautical miles northeast of Oman and all the crew were safe.

According to British maritime security firm Vanguard Tech, the vessel was sailing under a Liberian flag and "had been informed it had permission to transit the Strait of Hormuz".

But Iranian news agency Tasnim said the ship had "ignored warnings from Iran's armed forces".

In a separate incident, a cargo ship eight nautical miles west off Iran was fired upon and stopped in the water.

It was unclear who had targeted this ship.

"A master of an outbound cargo ship reports having been fired upon and is now stopped in the water. Crew are safe and accounted for. There is no reported damage to the vessel," UKMTO said.

Vanguard identified it as the Panama-flagged containership Euphoria, which it said was "transiting outbound of the Strait of Hormuz".

"It remains unclear whether she has resumed transiting," the firm said.

Marine Traffic showed that the ship was headed from the Jebel Ali port in the UAE to Jeddah in Saudi Arabia.

Shipping through the strategic Strait of Hormuz has been heavily restricted by Iran since the start of the war with Israel and the United States, while the US military is enforcing a blockade of Iranian ports.

US President Donald Trump announced Wednesday that the truce between the two countries would be extended after it first took effect on April 8.