A crew member raises the Iranian flag over the Adrian Darya 1 oil tanker, in the Strait of Gibraltar, Aug. 18, 2019. Photo: Reuters / Jon Nazca.

The US Treasury Department on Thursday warned that anyone around the world who helps fuel Iranian vessels blacklisted by Washington runs the risk of being designated as well.

The Treasury Department blacklisted the Adrian Darya, a tanker at the center of a confrontation between Washington and Tehran, on Aug. 30.

Washington has warned that it would regard any assistance given to the ship as support for a terrorist group, namely, Iran‘s Islamic Revolutionary Guard Corps. The US State Department has also said that any oil delivery to Syria from the tanker “enables the terrorism” of President Bashar al-Assad.

The ship, formerly called Grace 1, was detained by Britain off Gibraltar in July due to British suspicion it was carrying Iranian oil to Syria in violation of European Union sanctions.

In an update to its frequently asked questions, or FAQs, on Iran sanctions on its website, Treasury’s Office of Foreign Assets Control, or OFAC, said “the bunkering by non-US persons of an Iranian vessel that has been identified as blocked property of an Iranian person … and the making of related payments for these bunkering services — risk being designated themselves.”

The move outlines how the Trump administration is applying so-called secondary sanctions, or sanctions on entities in third party countries, in regards to the Iranian tanker and any other Iranian vessels it blacklists.

The Adrian Darya was released in mid-August after Iran told Britain its cargo was not headed to Syria. But the ship has been cruising the Mediterranean since its release and appeared to have turned off its transponder this week.

The Trump administration last year pulled out of a 2015 nuclear deal with Iran aimed at blocking its path to a nuclear bomb, and has ramped up sanctions to pressure and isolate Tehran.

OFAC said anyone helping to fuel an Iranian vessel that was transporting agricultural commodities, food, or medicine to Iran would not be exposed to sanctions, unless the transactions involved people already blacklisted by Washington.