US President-elect Donald Trump's "clear warning" to North Korea shows he is aware of the urgency of the threat posed by that state's nuclear program and will not waver from a policy of sanctions against the isolated country, South Korea says.
North Korean leader Kim Jong Un said on Sunday his nuclear-capable country was close to test-launching an intercontinental ballistic missile, raising the prospect of putting parts of the United States in range.
Trump dismissed the claim, saying on Twitter: "It won't happen."
South Korea's Foreign Ministry said Trump's comment, his first mention of the North Korean nuclear issue since the US election in November, could be interpreted as a "clear warning" to the North.
"Because of our active outreach, President-elect Trump and US officials are clearly aware of the gravity and urgency of the North Korean nuclear threat," ministry spokesman Cho June-hyuck said at a briefing on Tuesday.
"They are maintaining an unwavering stance on the need for sanctions on North Korea and for close cooperation between South Korea and the US."
The US State Department says it recognises that North Korea continues to pursue nuclear and ballistic missile technologies.
"We do not believe that at this point in time he has the capability to tip one of these (missiles) with a nuclear warhead ... but we do know that he continues to want to have those capabilities and the programs continue to march in that direction," State Department spokesman John Kirby told reporters.
Trump has not outlined a policy on North Korea, but during the election campaign indicated he would be willing to talk to its leader, given the opportunity.
Trump spokeswoman Kellyanne Conway told ABC's Good Morning America program that the president-elect was "putting North Korea on notice through this tweet and through other statements that this won't happen".
"He as president of the United States wants to stand between them and their missile capabilities, which experts say could be deployed to reach Seattle almost immediately," Conway said.
She says Trump has not publicly stated how he might respond to North Korea's nuclear weapons and missile programs and "won't before he's inaugurated".
"We do know that there are sanctions that are possible," Conway said.
"They haven't always worked. I think that China would have to have a significant role here as well."
Trump has been critical of China over the issue.
On Monday, he said China had benefited from its economic ties with the United States but would not use its influence to help control North Korea.
In response, Chinese Foreign Ministry spokesman Geng Shuang said China had been pushing for the denuclearisation of the Korean peninsula.
The UN Security Council imposed new sanctions on North Korea at the end of November after Pyongyang carried out its fifth and largest nuclear test so far in September.
