Separately, the US Treasury slapped sanctions on Tan and two companies he ran – Wee Tiong (S) Pte and WT Marine Pte, both of which did business with North Korea.

Tan “conducted illicit transactions totalling millions of dollars in support of North Korean entities in blatant violation of a host of economic sanctions the United States has established against North Korea and North Korean entities,” said FBI assistant director William Sweeney in a statement.

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The indictment and sanctions announcements said one of Tan’s companies handled millions of dollars worth of commodity contracts for Pyongyang, and said Tan followed instructions from sanctioned North Korean banks on how to move funds for them through the global banking system.

Money transfers involved front companies in Singapore, Thailand, Hong Kong and elsewhere, they said. They also said that ships operated by Tan’s WT Marine engaged in sanctions-violating activities involving North Korea.

The FBI placed Tan on its “most wanted” list, saying his whereabouts are currently unknown.

In Singapore, a Wee Tiong executive said in a phone interview that he had no knowledge about the company’s alleged dealings with North Korea.

“I am not in the position to say anything,” the man added, before abruptly hanging up. He refused to give his name.

Wee Tiong and WT Marine share the same director and address and have similar board members, official records show. Wee Tiong lists its activities as general wholesale trade. WT Marine describes itself as providing ship management services and operating barges, tugboats and freight “bumboats”.

Singapore officials had no immediate comment.

According to a 2015 article in the Singapore Straits Times and other public records, Tan was an up-and-coming businessman, the heir to his father’s commodities trading business, which had hundreds of millions of dollars in annual revenues.

In 2011, the year US authorities say he began laundering money for North Korea, he was named an “entrepreneur of the year” by Ernst and Young, the global business consultancy.

Prosecutors with the US attorney’s office in Manhattan allege that Tan used his Singapore-based trading firm and front companies in Thailand and Hong Kong to enable Daedong Credit Bank – a North Korean Bank blacklisted by the Treasury Department and the UN – to evade prohibitions on North Korean access to the US financial system.

Tan allegedly conducted transactions on Daedong’s behalf, laundered money for the bank and paid for the shipment of goods to North Korea.

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The indictment said Daedong made a US$380,000 payment to the trading firm through a Hong Kong front company in October 2016 that ran through a correspondent account at a US bank. The charges didn’t specify the total value of transactions in the case.

The Treasury’s action Thursday also included two Singapore-flagged vessels, the JW Jewel and the Nymex Star. The Jewel, an oil products tanker, was off the coast of Singapore on Thursday, according to Bloomberg ship-tracking data. There was no information available about the Star.

The sanctions and charges filed against Tan and his companies follow earlier allegations against other Singapore-based companies and highlight concerns over the role the trading hub may play in helping bypass sanctions against North Korea for its nuclear programme.

“Singapore has historically been a weak link in the enforcement of UN sanctions against North Korea and a key node in North Korea’s smuggling and money laundering operations,” said lawyer Joshua Stanton, who helped to draft the North Korea sanctions law.

Additional reporting by Bloomberg and Associated Press