The much-watched Iranian VLCC Adrian Darya 1 appears to have turned off its AIS in the eastern Mediterranean.
No satellite positioning update has been provided for 16 hours, when the 301,000-dwt tanker (built 1997) was underway, but awaiting orders, off Lebanon, near the Syrian border.
Speculation has been mounting that it will call in Syria or try to offload its crude cargo on to other smaller ships.
The former Grace 1 hit the headlines when it was seized in Gibraltar in July for allegedly attempting to take the oil to Syria, in breach of European Union sanctions.
But it was released in August after Iran pledged the crude would not go to Syria.
It has since sold its oil and registered destinations in Greece and Turkey before removing them.
Blacklisted
Over the weekend, the US blacklisted the vessel and its Indian master for “providing support to terrorism or acts of terrorism”.
The US Department of the Treasury’s Office of Foreign Assets Control (OFAC) said it took action against the tanker as it was “ultimately benefitting Iran’s Islamic Revolutionary Guard Corps-Qods Force (IRGC-QF).”
The US treasury said the vessel was “blocked property” under an anti-terrorist order. Captain Akhilesh Kumar was also blacklisted under the order.
US secretary of state Mike Pompeo had earlier said he had intelligence that the ship would head to the Syrian port of Tartus.
"It is now safe to assume she is in Syria's territorial waters," Tanker Trackers said on Twitter.
