North Korean leader Kim Jong Un has warned there will be consequences if the US "continues to break its promises and misjudges the patience of our people".
In a televised New Year address, he reaffirmed his resolve to completely denuclearise the Korean Peninsula, but said Pyongyang would have "no option to explore a new path" if sanctions and other pressures remain.
Mr Kim and Mr Trump met for the first time in Singapore in June but, despite a great deal of hype, the resulting agreements were vague on how denuclearisation would be achieved.
Nuclear talks between Washington and Pyongyang have stalled since then, and Mr Kim's New Year address has cast further doubt on whether he is willing to give up the weapons after all.
The North Korean leader did say he was willing to meet Mr Trump again – and said relations can "advance at a fast and excellent pace" if the US eases sanctions and halts joint military exercises with South Korea.
Wearing a black suit and a grey-blue tie, Mr Kim said: "Now that North and South Korea decided 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."
The US has thousands of troops in the region and, while some larger military exercises have been stopped, smaller ones continue. Sanctions have also been strengthened since the meeting with Mr Trump.
A meeting between North Korean officials and US secretary of state Mike Pompeo was cancelled by the North at the last minute in November and has yet to be rescheduled.
It is thought the North Koreans will push for a quick second summit, as they like their chances of winning concessions from Mr Trump that they might not get from lower-level officials.
Mr Kim congratulated himself on his diplomatic activities during 2018, including meetings with South Korean president Moon Jae-in and Chinese president Xi Jinping.
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But for most of his 30-minute speech, he focused on North Korea's economy and said he stands ready to resume projects with South Korea and restart operations at a jointly run factory park in the border town of Kaesong.
He also mooted the possibility of recommencing South Korean tours to the North's Diamond Mountain resort, something which is only achievable if sanctions are removed.