Tanker Seizures: What We Know

A court in Gibraltar is set to decide on Thursday the fate of a tanker carrying Iranian oil seized off the British territory in an operation involving Royal Marines.

The seizure is one of several in recent weeks that have ratcheted up tensions between Iran and its foe the United States and its allies.

Here's what we know about the vessels involved:

- Grace 1 -

Gibraltar police and customs officers aided by British Royal Marines intercepted the Grace 1 supertanker on July 4, as it passed through the strait between the territory on Spain's southern tip and North Africa.

Officials in Gibraltar and the United States suspect the 330-metre (1,000 foot) Panama-flagged ship was destined for Syria, in breach of separate sets of EU and US sanctions.

The Indian captain of the vessel, which was carrying 2.1 million barrels of oil, later told the BBC a military helicopter landed on its deck before the Royal Marines boarded.

Iran has called the seizure of the tanker "maritime piracy" and warned at the time that it would not let its detention go unanswered.

The Islamic republic has not officially disclosed the tanker's destination but it has repeatedly denied it was headed for Syria.

Gibraltar's supreme court announced on July 19 that it was extending the tanker's detention for 30 days.

- MT Riah - 

Iran's Islamic Revolutionary Guard Corps said its forces detained a "foreign tanker" in Gulf waters on July 14 for allegedly smuggling contraband fuel.

The tanker was seized south of the Iranian island of Larak in the strategic Strait of Hormuz, the Guards' official website said.

"With a capacity of two million litres and 12 foreign crew on board, the vessel was en route to deliver contraband fuel received from Iranian boats to foreign ships," it said.

TankerTrackers reported at the time that the Panamanian-flagged MT Riah, used in the strait for fuelling other vessels, had crossed into Iranian waters, and at that point its automatic identification system stopped sending signals.

- Stena Impero -

Revolutionary Guards surrounded the British-flagged Stena Impero with attack boats before rappelling onto the deck of the oil tanker in the Strait of Hormuz on July 19.

The 183-metre ship is impounded at the Iranian port of Bandar Abbas for breaking "international maritime rules" -- by allegedly failing to respond to distress calls and turning off its transponder after hitting a fishing boat.

Eighteen of the Swedish-owned tanker's 23 crew are Indian, and the rest are from the Philippines, Latvia, and Russia.

The seizure came hours after a Gibraltar court said it would extend the detention of the Grace 1.

Britain quickly called on Iran to release the Stena Impero, saying it was seized illegally in an "utterly unacceptable" gambit.

But Tehran said the seizure was a legal measure and further investigations were required, denying it was a tit-for-tat move as London suggested.

Iran and Britain have both so far ruled out the possibility of an oil tanker swap deal.

- Unknown vessel -

Iran seized another ship on July 31 with seven foreign crew onboard, claiming it was smuggling around 700,000 litres of fuel.

The Guards said the ship was transferred to Bushehr province and handed over to authorities, noting the vessel was en route to deliver fuel to Gulf Arab states.

The vessel's identity and the nationality of its crew were not revealed at the time of its seizure.