Two of the 10 companies just added to a United States blacklist for supporting the North Korean regime are based in Singapore.
Transatlantic Partners and Velmur Management helped provide oil to North Korea and attempted to use the US financial system to send millions of dollars in payments on behalf of North Korea-related transactions, the US Treasury said on Tuesday.
Russians Mikhail Pisklin, Andrey Serbin and Irina Huish were named as the main operators behind the two Singapore front companies.
Mr Pisklin, through Transatlantic, allegedly concluded a contract to buy fuel oil with Daesong Credit Development Bank, a sanctioned North Korean bank.
Mr Serbin and Ms Huish also allegedly bought gas oil for delivery to North Korea.
Transatlantic has been sanctioned for operating in North Korea's energy industry and Velmur for selling gas oil to North Korea.
The sanctions mean that no US citizens can deal with these firms or the three Russians connected to them.
Tansatlantic Partners was registered with the Accounting and Corporate Regulatory Authority (Acra) last May with a paid-up capital of $1,000. The address it uses at International Plaza is the office of MEA Business Consultancy.
Transatlantic's principal activity is selling equipment used in construction and industrial activity, according to filings with Acra.
Transatlantic's sole director and shareholder, Mr Andruew Tang You Liang, who is a pro-wrestler, told The Straits Times yesterday: "I do not have any information pertaining to the matter as I do not handle the day-to-day operations of the company and I am just a nominee shareholder."
Velmur Management is registered to an address at The Sail at Marina Bay, also the home address of one of its directors, South African Amtchentsev Vladen. It was registered with Acra in November 2014, with a paid-up capital of $1,000. The sole shareholder is Russian Ruslan Larin, who is also a director.
The US Treasury on Tuesday announced sanctions against six individuals and 10 organisations with financial ties to Pyongyang's weapons programme.
"It is unacceptable for individuals and companies in China, Russia and elsewhere to enable North Korea to generate income used to develop weapons of mass destruction and destabilise the region," US Treasury Secretary Steven Mnuchin said in a statement on Tuesday.
China reacted with irritation to the move, saying the US should "immediately correct its mistake" of imposing unilateral sanctions on Chinese companies and individuals.