President Trump is attacking China after a report claimed Chinese ships were illegally smuggling oil into North Korea.
A South Korean paper says China has been caught loading oil onto North Korean ships about 30 times since October, citing South Korean government sources and photos from U.S. satellites.
Trump tweeted he was "very disappointed that China is allowing oil to go into North Korea," arguing it undermined a peaceful solution to tensions on the peninsula. China has denied responsibility for the smuggling.
A United Nations resolution in September, supported by China, barred ship-to-ship transfers between North Korea and U.N. member states. The U.S. Treasury cited these transfers in a recent round of economic sanctions against the country.