The US Treasury warned against a "challenge" posed by Russia, citing its "malign conduct" and calling for a "firm and vigorous response." The sanctions, it says, were imposed due to an alleged violation of a ban on the ship-to-ship transfer of refined petroleum products with North Korea-flagged vessels.
On Tuesday, the United States slapped new sanctions on two Russian citizens, six Russia-flagged vessels and two other entities accused of facilitating the illegal transfer of petroleum products to North Korea.

"Today’s action against two entities and six vessels was taken pursuant to Executive Order 13810 of September 20, 2017, and targets persons involved in the ship-to-ship transfer of refined petroleum products with North Korea-flagged vessels, an activity expressly prohibited by the UN Security Council (UNSC)," the US Treasury said in a statement on its website.

The Treasury's Office of Foreign Assets Control (OFAC) designated two Russia-based shipping companies — Primorye Maritime Logistics Co Ltd. and Gudzon Shipping Co. LCC — along with the registered ship owners and managers of the Russia-flagged merchant vessel Patriot, the release said. Five Russia-flagged vessels — Neptun, Bella, Bogatyr, Partizan and Sevastopol — were also targeted, it added.