Vice-President Mike Pence is trying to counter North Korean "propaganda" around the Winter Olympics with his own symbolism and rhetoric, shining a spotlight on the North's nuclear weapons program and human rights abuses.
9 of 9 North Korean leader Kim Jong Un, in black, attends a military parade in Pyongyang, North Korea, on February 8, 2018. Moon has looked to the games as an opportunity to pursue a diplomatic opening with the North - a move Pence cautioned against.
Following Moon's statement, Pence told reporters that there were "many issues to discuss" between the USA and South Korea, chief among which is "our shared objective of the denuclearization of the Korean Peninsula".
Pence shied away from public criticism of Moon when they met Thursday evening, congratulating South Korea on hosting the games and pledging continued support in addressing the North's nuclear threat.
"Our resolve to stand with you is unshakable", Pence said.
But privately, officials said Pence expressed concern to Moon about his more conciliatory tone toward North Korea.
North Korea's Olympic delegations (graphic).
Aides acknowledged that the hard-nosed message is an unusual one for the affable Pence, but said the circumstances warrant the tone.
Kim Jong Un holds military parade before start of Olympics
"The U.S.is already opposing North Korea's development of nuclear weapons and intercontinental ballistic missiles, and U.N. Security Council resolutions have led to sanctions on North Korea", he said.
The Winter Olympics, which will take place just 80km south of the Demilitarized Zone that divides the two Koreas, have triggered a rapid rapprochement on the peninsula, although analysts warn that warmer relations may not last long beyond the games. At the same time, the vice president has deliberately left the door open to a possible encounter with North Korean officials expected to be in attendance.
Both Kim Yong-Nam, the North's ceremonial head of state, who is leading its delegation, and Mr Pence are due to attend the opening ceremony in Pyeongchang tomorrow, which could put them in the same room at a leaders' reception beforehand.
However, when asked on Thursday about the possibility of meetings between Pence or U.S. President Donald Trump's daughter, Ivanka, who will attend the closing ceremonies, and Kim's sister, White House spokesman Raj Shah told reporters in Washington: "There's no meetings planned whatsoever".
The regime had been planning the parade for weeks to mark the 70th anniversary of the founding of its military but instead of broadcasting it live, North Korea later aired an edited version on state-run television.
"To that end, I'm announcing today the United States of America will soon unveil the toughest and most aggressive round of economic sanctions on North Korea ever".
Kim Yo Jong is under USA sanctions for human rights abuses stemming from her role in the regime's mass censorship activities. "As allies, we will not allow the North Koreans to use the Olympics as a way to drive a wedge between us", a U.S. State Department spokeswoman, Katina Adams, said.
US, North Korea trade warnings on nuclear talks
It took aim at the Pentagon's proposal to develop a nuclear cruise missile that could be launched from a ship or submarine. US ally South Korea would not want to be the only Korea left without a nuclear device.