On Saturday, South Korea's President Moon Jae-in spoke by phone with Trump and agreed to maintain dialogue with Pyongyang
President Donald Trump warned Sunday that North Korea's Kim Jong Un had "everything" to lose through hostility towards the United States, after Pyongyang said it had carried out a major new weapons test.
"Kim Jong Un is too smart and has far too much to lose, everything actually, if he acts in a hostile way," Trump tweeted in response to the unspecified test at the Sohae space launch center.
The announcement of Saturday's test came just hours after Trump said he would be "surprised" by any hostile action from the North, emphasizing his "very good relationship" with Kim.
Trump and Kim engaged in months of mutual insults and threats of devastation in 2017, sending tensions soaring before a diplomatic rapprochement the following year.
The pair have met three times since June 2018 but with little progress towards denuclearization. Pyongyang has set Washington a December 31 deadline to make new concessions to kickstart stalled talks.
"North Korea, under the leadership of Kim Jong Un, has tremendous economic potential, but it must denuclearize as promised," Trump tweeted.
"Nato, China, Russia, Japan, and the entire world is unified on this issue!"
Writing that Kim had "signed a strong Denuclearization Agreement" at their June 2018 summit in Singapore," Trump warned: "He does not want to void his special relationship with the President of the United States or interfere with the U.S. Presidential Election in November."
Separately, interviewed on the CBS TV news program "Face the Nation," US National Security Advisor Robert O'Brien was asked whether North Korea was preparing to restart nuclear tests.
"I hope not. That would be a mistake on the part of North Korea," O'Brien said.
"Kim Jong Un promised to denuclearize North Korea," O'Brien said. "And we expect him to live up to the promise he made at the summit in Singapore. And we hope he'll do so."
On Saturday, South Korea's President Moon Jae-in spoke by phone with Trump and agreed to maintain dialogue with Pyongyang.
The 30-minute talk was the first conversation between Trump and the South Korean leader since they met at the UN General Assembly in New York in September.
"The two leaders shared an assessment that the current situation on the Korean peninsula is grave," said South Korean presidential spokeswoman Ko Min-jung, adding that Trump had requested the call.
A spokesman for North Korea's Academy of National Defence Science said Saturday's "very important test" would have an "important effect" on changing the "strategic position" of North Korea, in a statement carried by the official KCNA news agency.
The statement provided no further details on the test.