The United States on Tuesday slapped sanctions on two Russian shipping companies for violating UN Security Council resolutions by allegedly helping North Korea's illicit activities.

The Department of the Treasury announced that it added to its sanctions list two Russian shipping companies and six vessels involved in the banned ship-to-ship transfer of refined petroleum products to North Korea-flagged vessels. 

Treasury Secretary Steven Mnuchin said in a statement that ship-to-ship transfers with North Korea-flagged vessels from Russia or elsewhere of any goods being supplied, sold, or transferred to or from North Korea are prohibited under the UN Security Council resolutions on North Korea and are sanctionable under U.S. law. 

He added that consequences for violating these sanctions will remain in place until the U.S. has achieved the final, fully verified denuclearization of North Korea. 

Tuesday's announcement came just six days after Washington imposed sanctions on a Russian port service agency and Chinese companies for helping illicit shipments of alcohol, tobacco and cigarette products to the North.