Trump took to Twitter to suggest such sales would increase the chances of an armed conflict with Pyongyang.

Trump's tweet appeared to comment on a South Korean newspaper report , which said Chinese and North Korean ships were meeting at sea to hand off the oil.

“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.

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! — Donald J. Trump (@realDonaldTrump) December 28, 2017

The president sent the message from his golf club West Palm Beach, Fla., where he is spending the holidays.

The U.N. Security Council last week approved new sanctions designed to strictly limit North Korean imports of crude oil and refined petroleum products.

The sanctions came in response to a recent intercontinental ballistic missile test.

China denied making any oil sales to North Korea that violate U.N. sanctions.

Chinese Defense Ministry spokesman Ren Guoqiang said Thursday that Beijing is strictly enforcing the U.N. measures, according to Reuters.

“The situation you have mentioned absolutely does not exist,” Ren said when asked whether Chinese vessels were illegally providing oil to North Korea.

For months, Trump has pressured China to do more to isolate North Korea in an effort to persuade leader Kim Jong Un to drop his nuclear program.

China is North Korea's biggest trading partner, providing critical supplies of food and fuel to its neighbor.