Satellite photographs show six Chinese cargo ships engaging in trade with North Korea that is banned under UN sanctions, The Wall Street Journal has reported. United States officials claim the ships would turn off their tracking devices before entering North Korean ports to load cargo and turn them back on when en route to destinations in Russia and Vietnam.

The revelation threatens US-Chinese relations over the latter’s support of the North Korean regime. North Korea relies on coal sales to fund the luxurious lifestyles of its elite.

President Donald Trump recently complimented Chinese efforts to curb North Korean activities, although last year he said the opposite last year: the China does nothing but talk on North Korea.

Declassified intelligence reports reviewed by the WSJ shows that the ships picked up illegal cargo, primarily coal, in North Korea and transported it to Russia and Vietnam, or transferred it to other ships at sea.

The US presented the information to the United Nations, and asked the international body to ten cargo ships as sanctions violators. China permitted the UN to blacklist four ships that don’t have connections to China.

The WSJ used corporate records and shipping databases to identify the six ships owned by Chinese companies registered in Hong Kong. The Chinese government has investigated several of the cargo ships and at least one of the vessel’s managers has been arrested, according to the Wall Street Journal.

In December, the UN Security Council banned 90 percent of refined petroleum exports to North Korea, an action which the US supported.