WASHINGTON - US President Donald Trump and North Korean leader Kim Jong Un will meet next month (June) as scheduled, said South Korea's top security official.

The summit between the two leaders will take place despite fresh tensions on the Korean Peninsula, said Mr Chung Eui Yong, chief of the presidential National Security Office, reported Yonhap news agency.

He made the remarks aboard South Korea's Air Force One bound for Washington on Monday (May 21). South Korea President Moon Jae In is scheduled to meet Mr Trump on Tuesday.

"We believe there is a 99.9 per cent chance the North Korea-US summit (set for June 12 in Singapore) will be held as scheduled," Yonhap reported, quoting Mr Chung. "But we're just preparing for many different possibilities."

A historic inter-Korean summit in late April had raised hopes of reconciliation, but North Korea showed a dramatic change in tone in recent days, threatening to pull out of the high-level talks between Mr Kim and Mr Trump.

North Korea's chief negotiator Ri Son Gwon also said it would not hold talks with South Korea unless their demands were met, taking issue with the US-South Korean air combat drills known as Max Thunder, Reuters reported.

It came a day after it threatened to pull out of the summit with the US.

Asked about North Korea's about-face, Mr Chung said on Monday: "We're trying to understand the situation from the North's perspective."

Mr Chung also said that Mr Trump and Mr Kim will have "candid discussions on how to make the North (Korea)-US summit a success and produce significant agreements and how to best implement those agreements", Yonhap reported.

Mr Chung added that Seoul and Washington have been sharing information and have remained in close coordination with each other.

"We've had various working-level discussions on how to steer North Korea in a direction that we want, and I expect (Moon and Trump) will have great talks this time," he said, as reported by Yonhap.

Mr Chung also played down recent reports that Mr Trump had become nervous about meeting Mr Kim in Singapore next month for a historic summit meeting, The New York Times reported.

"We have perceived none of that," Mr Chung said, countering a New York Times report that cited Trump administration officials as saying that Mr Trump has begun pressing his aides and allies about whether he should take the risk of proceeding with a meeting with Mr Kim.

Mr Chung also denied that when Mr Trump called Mr Moon over the weekend, Mr Trump asked why the North's recent public statements seemed to contradict private assurances that Mr Moon had conveyed after he met Mr Kim on the inter-Korean border in late April.

"I listened in on the telephone conversation between the two heads of state, and no such thing happened," Mr Chung said.