The US is warning of the toughest sanctions that threaten private companies for assisting the crew of the Iranian tanker Adrian Darya (Grace 1), which is now in the Mediterranean Sea. Washington insists on the re-detention of the ship, the arrest of which was lifted by court order in Gibraltar, State Department’s representative said.

"The shipping sector is on notice that we will aggressively enforce U.S. sanctions," the official told Reuters days after warning countries not to allow the tanker to dock.

According to telemetry data, Adrian Darya is heading to the coast of Greece, although the country's prime minister has denied this information.

The tanker was detained off the coast of Gibraltar on suspicion of transporting oil to Syria, which is a violation of the EU sanctions regime.

Immediately after the court overturned the ship’s arrest order, a federal court in the US ordered the tanker to be detained on the basis of new circumstances, but Gibraltar did not comply with this requirement.