By Jake Kwon and James Griffiths, CNN

    (CNN) -- South Korea has seized a Hong Kong-registered ship that allegedly transferred oil to a North Korean vessel in violation of United Nations sanctions.

The South Korean Foreign Ministry said the Lighthouse Winmore left the port of Yeosu in South Korea carrying refined oil which was then transferred to a North Korean ship in international waters on October 19.

The US Treasury Department released satellite imagery in November of two ships allegedly performing an illegal ship-to-ship transfer in international waters on the same day.

It identified one of the ships as a sanctioned North Korean vessel, the Rye Song Gang 1, but did not name the other. The UN Security Council on Thursday added the Rye Song Gan 1 and three other vessels to a list of ships banned from docking at ports worldwide for breaching North Korea sanctions.

South Korean officials could not confirm Friday whether the second ship was the Lighthouse Winmore.

"UN Security Council sanctions prohibit the transfer of anything to a North Korean ship," a South Korean Foreign Ministry official told CNN, adding the Lighthouse Winmore was seized when it re-entered Yeosu on November 24.

US President Donald Trump said Beijing had been "caught red-handed," after the satellite images were republished in South Korean media earlier this week.

South Korea said the Lighthouse Winmore and its crew were still in South Korean custody and under investigation. There were 23 Chinese nationals and two Burmese nationals on board the ship, officials said, adding they would be permitted to leave only when the investigation was concluded.

China has denied breaching UN sanctions on North Korea.

The Lighthouse Winmore was one of 10 ships the United States asked the United Nations to ban from international ports this month over its alleged dealings with North Korea, according to Reuters.That move came after the United Nations blacklisted four ships in October, including one that was caught smuggling 30,000 North Korean-made rocket-propelled grenades in 2016.

According to South Korea, the Lighthouse Winmore was being leased by a Taiwanese company, the Billions Bunker Group, and was en route to Taiwan when it made a ship-to-ship transfer of its oil cargo to four ships, including one North Korean ship.

"This is one of the main ways in which North Korea uses an illegal network to circumvent UN Security Council sanctions," the South Korean Foreign Ministry spokesman said. It is customary in South Korea that officials do not give their names.

The Hong Kong government said in a statement Friday it had noted media reports that the Lighthouse Winmore had been seized. "We are liaising with the Korean parties concerned to obtain further information about the incident, and will take appropriate actions as necessary," the statement said.

'Very disappointed' in China

Chinese Foreign Ministry spokeswoman Hua Chunying on Friday reiterated that Beijing is enforcing all UN Security Council sanctions against North Korea, aimed at curbing Pyongyang's missile and nuclear weapons development.

In an interview with The New York Times, published Thursday, Trump claimed "oil is going into North Korea" and appeared to blame China, saying if Beijing fails to put pressure on Pyongyang then the United States may take punitive economic actions against Beijing.

"China on trade has ripped off this country more than any other element of the world in history has ripped off anything," Trump said.

"If they don't help us with North Korea, then I do what I've always said I want to do. China can help us much more, and they have to help us much more."

He added: "China's hurting us very badly on trade, but I have been soft on China because the only thing more important to me than trade is war."

A senior US State Department official told CNN on Thursday the United States is "aware that certain vessels have engaged in UN-prohibited activities, including ship-to-ship transfers of refined petroleum and the transport of coal from North Korea."

"We have evidence that some of the vessels engaged in these activities are owned by companies in several countries, including China," the official said. "We condemn these acts and hope that any UNSC members, including China, work more closely together to shut down smuggling activities."

Pyongyang has for years used deceptive shipping practices to help bring in revenue for the country's regime, analysts say, and the United States has called for more to be done to crack down on ships transporting goods to and from North Korea.

UN Security Council resolutions passed this year stipulate "all member states shall prohibit the entry into their ports of such designated vessels," save for some circumstances, including in emergencies or if they are granted humanitarian exceptions by the United Nations.

Correction: An earlier version of this story misstated the date of the seizure as December 24.

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