North Korean leader Kim Jong Un has warned there will be consequences if the United States "continues to break its promises and misjudges the patience of our people".
According to Sky News, Kim said: "Now that North and South Korea chose to take the path of peace and prosperity, we insist that joint military exercises with outside forces should no longer be allowed and deployment of war equipment such as outside strategic assets should be completely stopped". These are the Gaeseong industrial park in North Korea, where South Korean factories use North Korean labor, and the Mount Geumgang resort in North Korea.
The comments are likely to fuel growing scepticism over whether Pyongyang intends to give up the nuclear weapons program that it has long considered essential to its security.
He was referring to his landmark summit with US President Donald Trump in Singapore in June, when he said he had "fruitful talks" and "exchanged constructive ideas".
Kim directed part of his message at neighbor South Korea, urging it to ditch joint wargames with the U.S. for the sake of reconciliation.
Since the Trump-Kim summit though, less progress has been made than at least optimists had been hoping for.
A meeting between North Korean officials and U.S. secretary of state Mike Pompeo was cancelled by the North at the last minute in November and has yet to be rescheduled.
Kim's speech also points toward a hard year for the U.S.
United States officials say those initial steps were not confirmed and can be easily reversed, and have called for strict sanctions enforcement on the impoverished country until full, verifiable disarmament.
Wearing a black suit and a grey-blue tie, Mr Kim said: "Now that North and South Korea made a decision to take the path of peace and prosperity, we insist that joint military exercises with outside forces should no longer be allowed and deployment of war equipment such as outside strategic assets should be completely stopped".
In the joint declaration, Kim pledged to work towards the complete denuclearization of the Korean Peninsula, while in return, Trump promised to provide certain security guarantees to North Korea.
Duyeon Kim, from the Center for a New American Security, told CNN that the New Year's message was "confident" and "normal", but added that the message to the US was clear: "He still sent a very firm word of caution, bordering a nuanced threat, that if Washington doesn't keep its Singapore promise and continues with sanctions, then he has Plan B in mind and will go his separate way". Washington halted some large-scale military exercises with Seoul to aid nuclear negotiations, but smaller drills continued.
North Korea has not responded to Washington's calls for senior working-level talks to follow up on the June 12 summit, apparently preferring to engage Trump rather than other U.S. officials in its negotiations. Kim also met three times with Chinese President Xi Jinping, which boosted his leverage by reintroducing Beijing - Pyongyang's main ally - as a major player in the diplomatic process to resolve the nuclear standoff.
As a way to tackle chronic power shortages, he raised the need for atomic energy.
Kim Jong Un said Washington should stop breaking promises and lift sanctions - or Pyongyang may change path. Private analysts have accused North Korea of continuing nuclear and missile development, citing details from commercial satellite imagery.
"The US has no intention of easing our unilateral or United Nations sanctions", Stephen Biegun, the US special representative for North Korea said last month, noting that Washington, nevertheless, wants to explore other trust-building measures.