The US has blacklisted five companies, four connected ships and a North Korean firm based in Vietnam for violating international sanctions against North Korea.

Chinese manager Weihai Huijiang Trade, Vietnam-based Thinh Cuong and registered owners Good Siblings Ltd, Always Smooth Ltd and Silver Bridge Shipping were slapped with sanctions on Tuesday for their involvement in Pyongyang's coal trade.

Korea Daizin Trading was also sanctioned for arranging coal exports from North Korea to Vietnam.