"Today, I am announcing that we are launching the largest-ever set of new sanctions on the North Korean regime", Mr. Trump said in excerpts of a speech he was to deliver on Friday.
Speaking on condition of anonymity, officials earlier this week said a "task force" has been set up to address potential meddling in the 2018 congressional elections and work is underway to introduce more sanctions in response to Moscow's 2016 campaign. The actions block assets held by the firms and individuals in the United States and prohibit US citizens from dealing with them.
The United States steadily has been ratcheting up pressure on North Korean dictator Kim Jong-un to abandon his nuclear ambitions and ballistic missile program.
The Treasury Department, along with the U.S. Coast Guard and the State Department, also issued a worldwide advisory, warning countries of "significant sanctions risks" if they keep doing business with North Korea.
"Under current hard circumstances, we have chose to focus on whether peace on the Korean peninsula and improvement in inter-Korean relations can be derived from dialogue with (the visiting North Korean officials), not on their past or who they are", said Unification Ministry spokesman Baik Tae-hyun.
Moon said North Korea's participation in Olympics has "served as an opportunity for us to engage in active discussions between the two Koreas and this has led to lowering of tensions on the peninsula and an improvement in inter-Korean relations".
On December 28, Trump tweeted: "Caught RED HANDED - very disappointed that China is allowing oil to go into North Korea".
But were the Treasury Department designations of more than 50 companies and ships accused of illicit trading with the pariah nation really the toughest action yet by the US and the wider world?
USA leaders have been keen to stress that North Korea still poses a nuclear threat despite warming ties with the South.
The designations fit into the administration's larger strategy of economically and diplomatically isolating North Korea in an effort to drive it to denuclearize.
Mnuchin said at least one person on the list of oligarchs close to the Kremlin had already been targeted under a separate USA sanctions program.
Christopher Ford, assistant secretary of state for global security and non-proliferation, told reporters sanctions already had affected North Korea's weapons programs and this was shown by the lengths North Korea was going to try to evade sanctions.
Ivanka Trump, the president's daughter and adviser, is in South Korea for the closing ceremony of the games.
Moon also said it is important for South Korea and the United States to cooperate closely, the spokesperson said. In January Washington announced a round of sanctions and urged China and Russian Federation to expel North Koreans raising funds for the programs.
North Korea operates a fleet of 24 tankers capable of engaging in ship-to-ship transfers of refined petroleum products and other banned goods, Treasury said.
The new USA sanctions were unveiled during a visit to South Korea by Trump's daughter, Ivanka.
"President Moon also said out of all countries, South Korea has the strongest will to say it can not acknowledge North Korea as a nuclear state", he said. Its continued illicit ship-to-ship oil transfers, the official said, represent an effort to "make up that difference".