Seized UK-flagged tanker Stena Impero leaves Iranian port

Vessel was seized in July in move seen as retaliation for detention of Iranian ship in Gibraltar

A speedboat of Iran's Revolutionary Guard passes the British-flagged oil tanker Stena Impero in Bandar Abbas port, where the ship has been detained since July. Mizan News Agency via AP

The British-flagged Stena Impero tanker, detained by Iran in July, has started moving and left the Bandar Abbas port on Friday, according to ship-tracking data.

The Stena Impero was detained by Iran's Revolutionary Guard in the Strait of Hormuz waterway for alleged marine violations two weeks after Britain seized an Iranian tanker off the territory of Gibraltar. That vessel was released in August.

The Swedish-owned vessel set a new destination for Port Rashid in Dubai, about 250 kilometres away, tracking data showed. At normal tanker speed, it would reach Dubai within half a day.

Iran's marine and port authority said on its website that the Stena Impero was heading to international waters, hours after it began transmitting its location for the first time in weeks.

British Foreign Secretary Dominic Raab insisted after its release that the ship's detention had been illegal and that the UK would work with allies to safeguard shipping in the region.

"The Stena Impero was unlawfully seized by Iran. It is part of a pattern of attempts to disrupt freedom of navigation. We are working with our international partners to protect shipping and uphold the international rule of law," Mr Raab said.

The ship had been held at Bandar Abbas since being seized by Iran on July 19 for alleged violations that were not made clear. An Iranian government spokesman said on Monday that legal proceedings against the vessel had concluded.

“Based on a friendly approach that allows forgiving mistakes, ground for freedom of the tanker has been paved and it can move,” spokesman Ali Rabiei said.

Iran had earlier released seven of the ship's 23 crew members.

The ship's owners said the Stena Impero's detention "has meant enormous pressure for us all, especially for the crew".

Stena Bulk chief executive Erik Hanell told Sweden's TV4 channel that the ship seemed to be in good condition and "hopefully it will be on duty within a week or so."

"These ships cost about $20,000 a day, so it adds up to quite a lot," he said. "Money is important of course, but the focus is on the crew."

The seizure of the Stena Impero was seen as a retaliation for the seizure by British commandos of the Iranian tanker Grace 1 off the coast of Gibraltar on July 4.

Grace 1 was released by the British territory on August 18 after authorities in Gibraltar received written assurances from Iran it would not sell its cargo of 2.1 million barrels of oil in Syria, which is under European sanctions. After turning its tracker turned off, the vessel went on to sell the oil there regardless.

Tehran denied it had made any promises about the destination of the ship, which it renamed Adrian Darya 1. The United States had previously warned it would impose sanctions on any buyer of Iranian oil after the ship left the British territory.

The tit-for-tat seizures came amid increased tensions in the Arabian Gulf arising from the stand-off between Iran and the US. Washington blamed Iran for a series of mysterious attacks on oil tankers in the area and nearly launched retaliatory strikes on Iran after the Revolutionary Guard shot down a US drone. Iran's oil exports have been hit by stringent sanctions imposed by the US in response to Iran's missile development programme and support of proxy forces throughout the region.