U.S. President Donald Trump on Thursday expressed dissatisfaction with China over social media, following recent reports which claimed Chinese vessels were transferring oil products to North Korean ships at sea.

The comments on Twitter come after Beijing denied the reports on Wednesday, challenging journalists to find more convincing evidence of the claims which originated in South Korean media.

“Caught RED HANDED – very disappointed that China is allowing oil to go into North Korea. There will never be a friendly solution to the North Korea problem if this continues to happen!” Trump tweeted.

Unnamed government officials told South Korea’s Chosun