US President Donald Trump on Thursday said China has been "caught" allowing oil into North Korea and said such moves would prevent "a friendly solution" to the crisis over Pyongyang's nuclear program
"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 posted on Twitter.
China earlier on Thursday said there had been no UN sanction-breaking oil sales by Chinese ships to North Korea after a South Korean newspaper said Chinese and North Korean vessels had been illicitly linking up at sea to get oil to North Korea.
An official of the US State Department said the US government was aware of vessels engaged in such activity involving refined petroleum and coal.
"We have evidence that some of the vessels engaged in these activities are owned by companies in several countries, including China," the official said, speaking on condition of anonymity.
South Korea's Chosun Ilbo newspaper this week quoted South Korean government sources as saying that US spy satellites had detected Chinese ships transferring oil to North Korean vessels around 30 times since October.
US officials have not confirmed details of this report.
The Trump administration has led a drive to step up global sanctions on North Korea in response to Pyongyang's efforts to develop nuclear-tipped missiles capable of hitting the United States.
Washington says the full cooperation of China, North Korea's neighbour and main trading partner, is vital to the success of this effort, while warning that all options are on the table, including military ones, in dealing with North Korea.
The UN Security Council last week unanimously imposed new sanctions on North Korea for a recent intercontinental ballistic missile (ICBM) test, seeking to further limit its access to refined petroleum products and crude oil.
The US-drafted UN resolution seeks to ban nearly 90 per cent of refined petroleum exports to North Korea by capping them at 500,000 barrels a year.
It also caps crude oil supplies to North Korea at 4 million barrels a year and commits the Security Council to further reductions if Pyongyang conducts another nuclear or ICBM test.
Documents seen by Reuters in December showed Washington called on the Security Council to blacklist 10 ships for circumventing sanctions by conducting ship-to-ship transfers of refined petroleum products to North Korean vessels or transporting North Korean coal.
China and Russia subsequently asked for more time to consider the proposal.
In September, the Security Council put a cap of 2 million barrels a year on refined petroleum products exports to North Korea.
China has repeatedly said it is fully enforcing all resolutions against North Korea, despite suspicion in Washington, Seoul and Tokyo that loopholes still exist.
Asked at a regular briefing whether Chinese ships were illegally providing oil to North Korean ships, Chinese Defence Ministry spokesman Ren Guoqiang reiterated that China, including the military, strictly enforced UN resolutions.
"The situation you have mentioned absolutely does not exist," he said.