Donald Trump on Thursday said he was “very disappointed that China is allowing oil to go into North Korea” and said such moves would prevent “a friendly solution” to the crisis over Pyongyang’s nuclear program.

Earlier, China said there had been no sanction-breaking oil transfers between Chinese ships and North Korean vessels, of the kind described by a South Korea newspaper, Chosun Ilbo, which said spy satellites had detected 30 instances of such transfers since October.

That report was picked up by Fox News, commonly a source of information linked to Trump’s tweets.

“Caught RED HANDED,” the president wrote, with a characteristic use of capitals. “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 was spending another day in Florida, where he was staying at his Mar-a-Lago resort. Before the tweet was sent, the White House press pool reported that he had travelled to one of his golf courses in the state.

Trump has often departed from diplomatic niceties when discussing North Korea, both on Twitter and in speeches. In August, for example, he told reporters that if Pyongyang made any more threats to strike the US, it would “be met with fire and fury like the world has never seen”.

While repeatedly stressing that all options including military force are on the table, the president has routinely asked that China take responsibility for reducing the threat a nuclear North Korea poses, because it is the isolated nation’s primary trading partner.

In an illustrative tweet in April, he wrote: “China is very much the economic lifeline to North Korea so, while nothing is easy, if they want to solve the North Korean problem, they will.”

On Thursday, Rex Tillerson, the secretary of state, urged Beijing to exert “decisive economic leverage” on Pyongyang. “China has applied certain import bans and sanctions, but it could and should do more,” he wrote in the New York Times.

The UN security council last week unanimously imposed new sanctions on North Korea, in response to a recent intercontinental ballistic missile test. The US-drafted UN resolution seeks to ban nearly 90% of refined petroleum exports to North Korea by capping them at 500,000 barrels a year.

The resolution also caps crude oil supplies to North Korea at 4m barrels a year and commits the security council to further reductions if North Korea conducts another nuclear test or launches another ICBM.

Documents seen by Reuters this month showed that 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.

I've been saying it for a long, long time. #NoKo pic.twitter.com/LQl7tGhMdO — Donald J. Trump (@realDonaldTrump) December 28, 2017

In September, the security council put a cap of 2m 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, a 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.

A US state department official suggested on Wednesday that such transfers could still be going on.

“Ship-to-ship transfers … remain a concern as part of North Korea’s sanctions evasions activities,” the official said, while declining to provide details.

A state department spokesman, Michael Cavey, reiterated that the US had called on all countries to cut economic ties with North Korea.

“We urge China to end all economic ties with the DPRK, including tourism, and the provision of any oil or petroleum products, and expel all DPRK workers,” he said, using the acronym for North Korea’s official name, the Democratic People’s Republic of Korea.