On Thursday, the White House announced that it's slapping sanctions on a Chinese bank, a Chinese company, and two Chinese individuals for their ties to North Korea - an unambiguous sign that patience over China's reluctance to help curtail Pyongyang's nuclear program has grown thin.
In addition, Treasury's Office of Foreign Assets Control designated two Chinese individuals and one Chinese company in response to North Korea's ongoing WMD development and continued violations of UN Security Council resolutions.
China, which borders North Korea and is considered its only major ally, argues that negotiations are the best way to persuade it to halt its nuclear and missile activities.
"Without rewarding North Korea for its bad actions, South Korea and the United States should closely consult what they may give the North in return for a nuclear freeze", he said.
The Trump administration's months-long effort to be gentle in encouraging China to rein in North Korea is officially over.
Mnuchin said the decison will require U.S. banks to ensure that the Bank of Dandong does not access the USA financial system directly or indirectly through other foreign banks.
Mnuchin made clear that the United States is "in no way targeting China with these actions" and that USA officials "look forward to continuing to work closely with the government of China to stop the illicit financing in North Korea". The US's use of so-called "secondary" sanctions, which target firms and people doing business with North Korea rather than just North Korean firms and people themselves, is likely to make China's leaders pause and reconsider their usual tactic of dragging their feet on pressuring North Korea.
The comment came shortly after the death of Otto Warmbier, a US citizen who was detained in North Korea for more than a year and returned to his parents in a coma.
"The campaign is only now really gathering momentum", the official said.
The US Treasury Department on Thursday slapped sanctions on a Chinese bank over illicit activities in North Korea, including facilitating the production of weapons of mass destruction. He said those were "very effective and that's what brought them to the table".
All roads appear to lead to China.
"Treasurys Financial Crimes Enforcement Network has found the Bank of Dandong to be a foreign financial institution of primary money laundering concern under Section 311 of the USA PATRIOT Act", he said.
Anthony Ruggiero, a sanctions expert and former Treasury Department official, described it as a small Chinese bank "sitting at the heart" of trade between North Korea and China.
"If Trump wants to get serious about applying greater pressure on North Korea, at this point that will require a more coercive attitude toward China", Ratner said.