"Caught RED HANDED - very disappointed that China is allowing oil to go into North Korea", Mr Trump wrote in a post on Twitter.
Such ship-to-ship trades are banned under a UN Security Council resolution adopted in September, but according to South Korean government sources, American satellites have pictured large vessels from both China and North Korea illegally trading in a stretch of the West Sea on multiple occasions.
U.S. satellites have spotted Chinese tankers transferring oil to North Korean ships 30 times in three months - despite strict United Nations trade embargoes, according to reports.
US President Donald Trump has accused China of being caught "red-handed" selling oil to North Korea, saying such moves would prevent "a friendly solution" to the crisis over Pyongyang's nuclear program. One of them - Rye Song Gang 1, seen "connected to a Chinese vessel" - was included in the November 21 sanctions as a vessel of Korea Kumbyol Trading Company possibly transferring oil to evade sanctions.
But she said China has "completely and strictly" enforced trade restrictions aimed at discouraging North Korea from developing nuclear and missile technology.
The U.N. resolution seeks to ban almost 90 per cent of refined petroleum exports to North Korea by capping them at 500,000 barrels a year.
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According to the most recent Chinese customs data released Tuesday, the country did not export gasoline, jet fuel, diesel or fuel oil to Pyongyang in November.
The U.S. -drafted resolution also caps crude oil supplies to North Korea at 4 million barrels a year and commits the Council to further reductions if it were to conduct another nuclear test or launch another ICBM.
USA spy satellites have captured images of what appears to be Chinese ships illegally selling oil to North Korean boats.
The satellite pictures even show the names of the ships.
US President Donald Trump has reacted to reports on China's alleged oil exports to North Korea, violating the December 22 United Nations trade restrictions introduced against the country, limiting their oil deals to four billion barrels per year.
China and Russian Federation subsequently asked for more time to consider the proposal.