The Trump administration did not respond to queries to explain what Trump meant in his tweet for more than five hours.
Klingner said Trump's move signalled that his "maximum pressure" sanctions campaign on North Korea was not going to get any stronger and recalled an announcement the president made before a first summit with Kim in June previous year when he said he was putting a large list of planned sanctions on hold. "And it seems to me this takes everything to a new level of dysfunction that if the president can tweet something about his own policy on sanctions and nobody quite understands what it means, how do you run foreign policy?"
White House spokeswoman Sarah Sanders didn't elaborate on the sanctions, justifying the president's action by citing his personal relationship with North Korean leader Kim Jong Un.
Analysts, as well as North Korean officials, have pointed to the presence of White House national security adviser John Bolton, a vocal hawk against Pyongyang, at the negotiating table just prior to the talks collapsing. Those sanctions prompted swift pushback from the Chinese and North Korea governments.
"Everyone should take notice and review their own activities to ensure they are not involved in North Korea's sanctions evasion", he said.
The Treasury Department sanctioned Dalian Haibo International Freight and Liaoning Danxing International Forwarding for using deceptive methods to circumvent international and United States sanctions and the U.S. commitment to implementing existing UN Security Council resolutions.
"Treasury will continue to enforce our sanctions, and we are making it explicitly clear that shipping companies employing deceptive tactics to mask illicit trade with North Korea expose themselves to great risk", Mnuchin said.
But she did not specify which sanctions Trump spoke of.
The Treasury Department said Thursday that the USA was slapping new sanctions on two Chinese shipping companies accused of aiding North Korea - and a day later, President Trump canceled them. "Everyone over here is watching Twitter and the news". For now, they are simply in a holding pattern.
The sanctions on the Chinese shippers were the first since the second US-North Korea summit broke down last month.