A second oil tanker has been seized by Iran in the Strait of Hormuz.

The US Navy said the 309,164-dwt VLCC Niovi (built 2005) was swarmed by Iranian Revolutionary Guard Corps fast attack vessels around 6:20 am local time (0220 GMT) after leaving Dubai and heading towards Fujairah.

The ships were said to have forced the vessel to reverse course to Fujairah and towards Iranian territorial waters.

Security company Ambrey said the tanker was heading southbound in Omani territorial waters, approximately 47 nautical miles south of Bandar Abbas in Iran.

US navy footage showed 11 small boats approaching the vessel.

The tanker had an estimated freeboard of 21.25 metres at the time.

The VLCC had last called at Port Rashid in the UAE.

Ambrey observed the AIS signal going offline at 0231 UTC on 3 May.

“This aligned with US reports that stated the vessel was seized at approximately 0220 UTC,” the company said.

Iranian state news outlets confirmed the seizure. A public prosecutor in Tehran said in the reports that the vessel was impounded by the Revolutionary Guard on a judicial order issued after “a complaint by a plaintiff”.

“Iran’s continued harassment of vessels and interference with navigational rights in regional waters are unwarranted, irresponsible and a present threat to maritime security and the global economy,” US Naval Forces Central Command said in a statement.

Tit-for-tat again?

The Niovi’s reported seizure comes six days after the 159,000-dwt Advantage Sweet (built 2012) seizure by Iran.

Tehran said the suezmax tanker struck an Iranian fishing boat, but several sources have said the seizure was retaliation for US courts issuing an order to seize a second aframax, the 159,000-dwt Suez Rajan (built 2011), which is said to have been carrying Iranian oil.

Greek authorities had issued a warning that its shipping was at an increased risk from Iran after the detention of the Suez Rajan.

The US Navy said it was the 15th instance of Iranian forces harassing, attacking or interfering with merchant vessels over the last two years.

The Niovi’s registered owner is Grand Financing Co, according to shipping database Equasis, which shares a Piraeus address with commercial and technical manager Smart Tankers.

Managers at Smart Tankers, a venture of the Bakos and Kaimenakis families, were not immediately available for comment.

According to Greek coastguards, the Niovis's crew consists of 30 seafarers. All of them are from the Philippines and Sri Lanka with the exception of its master, who is a Greek citizen born in 1970.

Greek authorities will intervene with Iranian authorities on behalf of the master.

According to AIS data, the Niovi’s destination was set to Fujairah.

Tracking data shows the ship’s last broadcast was roughly 23 km (12.3 nautical miles) north of the tip of the United Arab Emirates.

About a fifth of the world’s crude oil and oil products passes through the Strait of Hormuz, a narrow choke point between Iran and Oman, according to data from analytics firm Vortexa.

Harry Papachristou contributed to this story.