An Iranian tanker that sparked a diplomatic standoff between Tehran and western states has been spotted off the coast of Syria according to US officials – despite assurances the vessel would not deliver its 2.1 million barrels of crude oil to the country.

British royal marine commandos had previously detained the Adrian Darya 1 – then called the Grace 1 – off the coast of Gibraltar in July amid concerns it was being used to transport crude oil to Syria, sidestepping European Union sanctions on the country.

The vessel was released following written assurances from Tehran that it would not deliver the oil to the country.

However, after appearing to have turned off radio trackers in the eastern Mediterranean on Monday, satellite imagery has shown the vessel two nautical miles from the port of Tartus, western Syria, according to US officials.

Donald Trump's National Security Advisor John Bolton has since claimed that those who had believed the ship would not continue on to the country were “in denial”, following a continued campaign from Washington to seize the vessel.

The US Treasury Department blacklisted the tanker on Friday after warnings from Washington that any nation assisting the Adrian Darya 1 would be viewed as showing support for a terror organisation – specifically Iran’s Islamic Revolutionary Guard Corps.

In photos: British-flagged tanker seized by Iran Show all 13 1 /13 In photos: British-flagged tanker seized by Iran In photos: British-flagged tanker seized by Iran A speedboat of Iran's Revolutionary Guard moving around the British-flagged oil tanker Stena Impero Tasnim News Agency/AP In photos: British-flagged tanker seized by Iran Crew members of the British-flagged tanker Stena Impero, that was seized by Iran in the Strait of Hormuz EPA/IRIB News Agency In photos: British-flagged tanker seized by Iran A satellite image of the Iranian port city of Bandar Abbas reveals the presence of the seized British oil tanker, the Stena Impero on July 22 Maxar Technologies/Reuters In photos: British-flagged tanker seized by Iran Iranian Revolutionary Guard Corps (IRGC) claims to have seized Stena Impero at the Strait of Hormuz with 23 crew on board on 20 July EPA/IRIB News Agency In photos: British-flagged tanker seized by Iran Iranian Revolutionary Guards patrolling around the captured British-flagged tanker Stena Impero as it's anchored off the Iranian port city of Bandar Abbas AFP/Getty In photos: British-flagged tanker seized by Iran epa07733612 A handout photo made available by Iranian state-run IRIB News Agency on 22 July 2019 shows crew members of the British-flagged tanker Stena Impero, that was seized by Iran in the Strait of Hormuz on 19 July 2019. Iranian Revolutionary Guard Corps (IRGC) claims to have seized Stena Impero at the Strait of Hormuz with 23 crew on board on 20 July 2019. EPA/IRIB NEWS AGENCY / HANDOUT HANDOUT EDITORIAL USE ONLY/NO SALES IRIB NEWS AGENCY / HANDOUT EPA/IRIB News Agency In photos: British-flagged tanker seized by Iran A satellite image of the Iranian port city of Bandar Abbas reveals the presence of the seized British oil tanker, the Stena Impero on July 22 Maxar Technologies/Reuters In photos: British-flagged tanker seized by Iran A speedboat of the Iran's Revolutionary Guard moves around a British-flagged oil tanker Stena Impero AP In photos: British-flagged tanker seized by Iran epa07733614 A handout photo made available by Iranian state-run IRIB News Agency on 22 July 2019 shows crew members of the British-flagged tanker Stena Impero, that was seized by Iran in the Strait of Hormuz on 19 July 2019. Iranian Revolutionary Guard Corps (IRGC) claims to have seized Stena Impero at the Strait of Hormuz with 23 crew on board on 20 July 2019. EPA/IRIB NEWS AGENCY / HANDOUT HANDOUT EDITORIAL USE ONLY/NO SALES IRIB NEWS AGENCY / HANDOUT EPA/IRIB News Agency In photos: British-flagged tanker seized by Iran In this photo released by state-run IRIB News Agency, which aired on Monday, July 22, 2019, shows cooks in the galley of the British-flagged tanker Stena Impero that was seized by Tehran in the Strait of Hormuz on Friday. The Associated Press cannot independently verify the condition of the crew members, but in the video they looked to be in good health and it didn't appear as though they were being filmed under duress. (IRIB News Agency via AP) AP In photos: British-flagged tanker seized by Iran epa07733619 A handout photo made available by Iranian state-run IRIB News Agency on 22 July 2019 shows crew members of the British-flagged tanker Stena Impero, that was seized by Iran in the Strait of Hormuz on 19 July 2019. Iranian Revolutionary Guard Corps (IRGC) claims to have seized Stena Impero at the Strait of Hormuz with 23 crew on board on 20 July 2019. EPA/IRIB NEWS AGENCY / HANDOUT HANDOUT EDITORIAL USE ONLY/NO SALES IRIB NEWS AGENCY / HANDOUT EPA/IRIB News Agency In photos: British-flagged tanker seized by Iran epa07733613 A handout photo made available by Iranian state-run IRIB News Agency on 22 July 2019 shows crew members of the British-flagged tanker Stena Impero, that was seized by Iran in the Strait of Hormuz on 19 July 2019. Iranian Revolutionary Guard Corps (IRGC) claims to have seized Stena Impero at the Strait of Hormuz with 23 crew on board on 20 July 2019. EPA/IRIB NEWS AGENCY / HANDOUT HANDOUT EDITORIAL USE ONLY/NO SALES IRIB NEWS AGENCY / HANDOUT EPA/IRIB News Agency In photos: British-flagged tanker seized by Iran epa07733616 A handout photo made available by Iranian state-run IRIB News Agency on 22 July 2019 shows crew members of the British-flagged tanker Stena Impero, that was seized by Iran in the Strait of Hormuz on 19 July 2019. Iranian Revolutionary Guard Corps (IRGC) claims to have seized Stena Impero at the Strait of Hormuz with 23 crew on board on 20 July 2019. EPA/IRIB NEWS AGENCY / HANDOUT HANDOUT EDITORIAL USE ONLY/NO SALES IRIB NEWS AGENCY / HANDOUT EPA/IRIB News Agency

Writing on Twitter, Mr Bolton added: “Tehran thinks it’s more important to fund the murderous Assad regime than provide for its own people. We can talk, but Iran’s not getting any sanctions relief until it stops lying and spreading terror”

The detaining of the vessel by UK authorities became a flash point in tensions between Iran, the US and the EU as the Middle Eastern state looks to fight back against tough sanctions levied by Washington after the breakdown of the Iran nuclear deal.

In an apparent show of retaliation for the Adrian Darya’s detention in Gibraltar, Iran seized a British-flagged tanker, the Stena Impero, two weeks later for alleged marine violations. So far the state has released seven of the ship’s crew, with a further 16 still left aboard.

And on Saturday the Iranian coast guard seized a vessel carrying 284,000 litres of diesel for allegedly smuggling fuel in the Gulf, detaining 12 crew members from the Philippines in the process.