Iranian gunboats approach US tanker in Strait of Hormuz

British maritime security firm Vanguard Tech said Tuesday that a US-flagged tanker was approached and challenged by Iranian gunboats in the Strait of Hormuz, before continuing on its way.

The Stena Imperative was approached by three pairs of small armed boats belonging to the Revolutionary Guards while transiting the strait approximately 16 nautical miles (30 kilometres) north of Oman, the company said. 

The gunboats hailed it by radio, ordering the captain "to stop the engines and prepare to be boarded", but the ship increased speed and maintained course, the firm added, stressing it did not enter Iranian territorial waters.

"The vessel is now being escorted by a US warship," Vanguard Tech said. 

Earlier, the British maritime security agency UKMTO reported the incident without specifying the nationality of the ship or the boats that approached it. 

The Iranian news agency Fars said a vessel, whose nationality it did not specify, had entered the country's territorial waters in the Strait of Hormuz illegally, at which point Iranian units "requested" that it present the necessary permissions.

"The vessel had no legal authorisation to be in these waters," Fars said. "It was therefore warned and immediately left Iranian waters."

The strait, a key passage for the global transport of oil and liquefied natural gas, has been the scene of several incidents in the past. 

A senior Iranian official from the naval forces of the Revolutionary Guards, the ideological army of the Islamic republic, threatened last week to block the passage in the event of a US attack.