SEOUL/WASHINGTON (Reuters) - U.S. President-elect Donald Trump’s “clear warning” to North Korea shows he is aware of the urgency of the threat posed by North Korea’s nuclear program and will not waver from a policy of sanctions against the isolated country, South Korea said on Tuesday.

U.S. President-elect Donald Trump delivered brief remarks to reporters at the Mar-a-lago Club in Palm Beach, Florida, U.S. December 28, 2016. REUTERS/Jonathan Ernst - RTX2WSA9

North Korean leader Kim Jong Un said on Sunday his nuclear-capable country was close to test-launching an intercontinental ballistic missile (ICBM), 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 U.S. election in November, could be interpreted as a “clear warning” to the North.

“Because of our active outreach, President-elect Trump and U.S. officials are clearly aware of the gravity and urgency of the North Korean nuclear threat,” ministry spokesman Cho June-hyuck said at a briefing.

“They are maintaining an unwavering stance on the need for sanctions on North Korea and for close cooperation between South Korea and the U.S.”

The U.S. State Department said it recognized that North Korea continued 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 U.S. election campaign indicated he would be willing to talk to its leader, Kim, 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 said Trump had 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 denuclearization of the Korean peninsula.

“China’s efforts in this regard are perfectly obvious,” Geng told a news briefing. “As a permanent member of the U.N. Security Council we have proactively participated in relevant discussions on the North Korean nuclear issue and have jointly passed several resolutions with other parties.

“This shows China’s responsible attitude.”

Asked about Trump’s view that China was not helping to contain North Korea’s nuclear ambitions, the State Department’s Kirby said: “We would not agree with that assessment.”

The United States has for years dismissed North Korean calls for talks, insisting it must disarm first.

The United States and ally South Korea have responded to two North Korean nuclear tests and various missile tests last year with ever-more-severe sanctions.

The U.N. 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.

A North Korean ICBM, once fully developed, could threaten the continental United States, which is about 9,000 km (5,500 miles) from the North.

ICBMs have a minimum range of about 5,500 km (3,400 miles), but some are designed to travel 10,000 km (6,200 miles) or further.

North Korea worked last year on developing components for an ICBM, saying it was close to a test-launch plausible, international weapons experts said on Monday.