A Venezuela-linked oil tanker seized by the US has been spotted off the coast of Moray in Scotland a week after it was intercepted.
The Marinera, a Russian-flagged vessel previously known as Bella-1, was witnessed being escorted to an undisclosed location accompanied by a US coast guard vessel.
It comes as British special forces could be given the green light to raid the vessels in a move to place further pressure on Russian president Vladimir Putin, according to reports.
The use of shadow fleet tankers to move sanctioned oil around the world has increased in recent years as states seek to circumvent restrictions to their transportation.
Maritime law states they must be registered to a specific country or territory and display its flag. But if a ship fails to do this, it could be deemed stateless. Nationality has to be established for the UK to seize a vessel.
Shadow fleets often operate under deceptive practices including the use of fake flags.
But where are they travelling?
European waters
It is difficult to determine the locations of the vessels for certain, but data collated by FleetLeaks shows the real-time position and compliance status of over 400 vessels operating under international sanctions.
It shows several ships operating in the North Sea in the regions between the UK, Denmark, Sweden, Norway and the Netherlands, flying the flags of Oman and Sierra Leone.
Several vessels are operating in the Baltic Sea in waters bordering Sweden, Poland, Lithuania, Latvia, Estonia and Denmark.
Others are passing through the Norwegian Sea. The US military and Coast Guard intercepted the Marinera in the waters northwest of Scotland after a two-week chase through the North Atlantic.
According to Shadow Fleet tracker, the vast majority of Russian-linked vessels operate along this region.
Southeast Asia
Other hotbeds of shadow fleet activity include the Singapore Strait and South China Sea, situated between the isles of Indonesia and Singapore. The tracker records around 44 shadow fleet vessels in this region. A handful seem to be operating around the Indian Ocean.
The Philippines Sea and Pacific Ocean also recorded around 50 vessels, according to FleetLeaks. The ships appear to be operating off the coast of China, Japan and North and South Korea.
North Africa and the Middle East
Shadow Fleet also shows several Russia-linked shadow fleet ships along the coasts of Israel and Turkey in the Mediterranean Sea.
South America
Although the trackers do not appear to show any shadow fleet activity around the coasts of South America at the moment, however the US military did seize an oil tanker in international waters around the coast of Venezuela ahead of the capture of Nicolas Maduro.
How have the British government reacted?
Soldiers could target illegal oil tankers in a move to place further economic pressure on Putin. The briefing came days after the UK supported a US operation to seize the Marinera.
A defence source confirmed to The Times that options to seize further vessels are being considered. No timeframe has been given for potential missions, but the Special Boats Service (SBS) would likely lead the raids.
A spokeswoman for the Department for Transport: “Deterring, disrupting and degrading the Russian shadow fleet is a priority for this government. Alongside our allies, we are stepping up our response to shadow vessels – and we will continue to do so.”
“The government also affirmed its commitment to work with allies to “disrupt and deter shadow fleet vessels and their harmful maritime activity.”
Defence Secretary John Healey has publicly justified the action to seize the Marinera, saying: “This ship, with a nefarious history, is part of a Russian-Iranian axis of sanctions evasion which is fuelling terrorism, conflict and misery from the Middle East to Ukraine.”
