The head of the shipping firm that owns the British-flagged oil tanker held by Iran since July has said it is still in Iranian waters, a day after Tehran said the vessel was free to move.

Erik Hanell, chief executive of Swedish company Stena Bulk, told the Associated Press: “We know nothing as to why she is still there.”

Iran’s official IRNA news agency quoted the head of the country’s marine and ports authority, Mohammad Rastad, as saying the Stena Impero “will soon” leave Iranian waters but the timing depends on finalising “legal” procedures.

Mr Hanell responded: “Despite public statements by Iranian authorities over the past three days that judicial proceedings have concluded, and the Stena Impero is free to leave Iran, the vessel remains detained at anchor in Bandar Abbas.

“We continue to work hard to secure the release of the crew and vessel.”

Iran Persian Gulf Tensions
A speedboat of Iran’s Revolutionary Guard passes the Stena Impero (Hasan Shirvani/Mizan News Agency/AP)

On Monday, Iranian government spokesman Ali Rabiei told journalists that legal proceedings against the Stena Impero had ended. The tanker has been kept in the Iranian port of Bandar Abbas since July 19.

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

Iran seized the tanker in the Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20% of the world’s oil passes.

The raid saw commandos drop on to the ship from a helicopter, carrying assault rifles, with dramatic images later replayed on state television.

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(PA Graphics)

Earlier this month, Iran released seven of the ship’s crew members, but 16 remain on board.

The seizure came after authorities in Gibraltar seized an Iranian tanker carrying 130 million dollars (£104 million) in crude oil on suspicion of it breaking European Union sanctions on Syria.

Gibraltar later released the tanker, then called the Grace 1, after it said Iran had promised the ship would not go to Syria.

The ship, renamed the Adrian Darya 1, now sits off the Syrian coast, angering Britain. Iran has not said who purchased its 2.1 million barrels of crude oil.

The ship seizures came after months of heightened tensions in the Persian Gulf, sparked by President Donald Trump’s decision over a year ago to withdraw from Iran’s nuclear deal with world powers and impose crippling sanctions on its vital oil trade.

Iran since has begun breaking terms of the deal.