The US Department of Treasury’s Office of Foreign Assets Control on Tuesday announced sanctions against six trading companies and four vessels over their involvement in North Korea’s illicit trade of coal.

The OFAC’s latest move, which comes a day after a US newspaper published US government-provided satellite photos indicating coal trade between North Korea and China, appears to be the Trump administration’s message to Pyongyang that it will not loosen the reins until its end.

China-based Weihai Huijiang Trade, Always Smooth and Good Siblings, the latter two of which are also registered in the UK; Hong Kong-based Silver Bridge Shipping Co-HKG; Pyongyang-based Korea Daizin Trading; Vietnam-based Thinh Cuong Co.; and four vessels -- Lucky Star, The Asia Bridge, Calm Bridge and Star 18 -- have now been blocked under existing US executive orders.

The latest sanctions “address the transportation and exportation of North Korean coal in violation of UN Security Council resolution 2371 and underscore that entities within the People’s Republic of China have continued to engage in activities prohibited under the UNSCRs,” the Treasury Department said in a press release.

“PRC authorities must implement and enforce the UNSCRs, including by taking action against companies, individuals and vessels that engage in UNSCR-prohibited trade including the procurement of North Korean coal.”

Daizin Trading, a company operating in North Korea and Vietnam, has exported coal from North Korea since as early as mid-2016, lied at least once that the coal is of Russian origin, and has transported thousands of tons of coal and iron ore to Vietnam, the Treasury Department said.

Other designated companies own or control the designated vessels that loaded coal at North Korean ports such as Wonsan and Songnim, and transported their cargo “throughout the region,” according to the Treasury Department.

“The DPRK continues to circumvent the UN prohibition on the exportation of coal, a key revenue generator that helps fund its weapons of mass destruction programs,” US Secretary of Treasury Steven Mnuchin was quoted as saying in the press release, referring to the North’s official name, the Democratic People’s Republic of Korea.

“The North Korean regime often uses forced labor from prison camps in its mining industries, including coal, exploiting its own people to advance its illicit weapons programs.”

The Treasury Department said the latest actions were also undertaken “in the spirit of” a sanctions law named after Otto Warmbier, an American college student who was imprisoned in North Korea, and died soon after he was released in a vegetative state.

Trump’s national security adviser Robert O’Brien also said in a media interview released Monday that China has been very lax on the transfer of coal and other commodities out of North Korea, and called on Beijing to fully live up to its obligations as a UN member.

By Kim So-hyun (sophie@heraldcorp.com)