On 23 February 2018 the US Government announced a large sanctions package targeting both North Korean and third-country* shipping and trading companies and their vessels to further disrupt and isolate North Korea.
*Such as China, Hong Kong and Singapore.

Pursuant to Executive Order 13810 (EO 13810), 16 North Korean shipping companies have been designated and 19 of their North Korean flagged vessels have been blocked.

Also pursuant to EO 13810, the US has sanctioned nine international third-country  shipping companies and nine of their vessels which are accused of exporting coal from North Korea and/or engaging in prohibited ship-to-ship transfers of various petroleum products.

Pursuant to Executive Order 13722 (EO 13722) a Taiwanese citizen, a Taiwanese company and a Taiwan and Marshall Island based company have also been designated for coordinating coal exports and brokering oil deals.

A full list of the newly sanctioned individuals, companies and vessels can be found at:
https://home.treasury.gov/news/press-releases/sm0297

The US Department of the Treasury’s Office of Foreign Asset Control also issued an advisory alerting interested parties to the significant sanctions risks to those continuing to enable shipments of goods to and from North Korea. The advisory covers known deceptive practices used by North Korean companies to evade sanctions. These include falsifying and concealing information displayed on vessels, ship-to-ship transfers and disabling or manipulating Automatic Identification Systems (AIS). The advisory note can be found at:
https://www.treasury.gov/resource-center/sanctions/OFAC-Enforcement/Documents/dprk_vessel_advisory_02232018.pdf