WASHINGTON • United States President Donald Trump said he would be very disappointed in North Korean leader Kim Jong Un if reports about rebuilding at a rocket launch site in North Korea were true.

Two US think-tanks and South Korea's Yonhap news agency reported that work was under way to restore part of North Korea's Sohae Satellite Launching Station, even as Mr Trump met Mr Kim at a second summit in Hanoi last week.

"I would be very disappointed if that were happening," Mr Trump told reporters in the Oval Office on Wednesday, when asked if North Korea was breaking a promise.

"Well, we are going to see. It is too early to see... It is a very early report. We are the ones that put it out. But I would be very, very disappointed in Chairman Kim, and I don't think I will be, but we will see what happens. We will take a look. It will ultimately get solved."

A second summit between Mr Trump and Mr Kim broke down last week in Hanoi over differences on how far North Korea was willing to limit its nuclear programme and the degree of US willingness to ease sanctions.

"We have a very nasty problem there. We have to solve a problem," Mr Trump said, while adding in apparent reference to Mr Kim: "The relationship is good."

Mr Trump, eager for a big foreign policy win on North Korea that has eluded his predecessors for decades, has repeatedly stressed his good relationship with Mr Kim.

He went as far late last year as to say that they "fell in love", but the bonhomie has failed so far to bridge the wide gap between the two sides.

US National Security Adviser John Bolton had earlier warned that new sanctions could be introduced if North Korea did not scrap its nuclear weapons programme, but said yesterday that Mr Trump is open to additional talks with North Korea over denuclearisation.

The breakdown of the Feb 27 and 28 summit and Mr Bolton's sanctions threat have raised questions about the future of the dialogue the Trump administration has pursued in an effort to persuade North Korea to abandon a nuclear weapons programme that threatens the US.

White House spokesman Sarah Sanders said on Wednesday that the US was "continuing to have ongoing conversations with North Korea", but did not elaborate.

Meanwhile US Special Representative for North Korea Stephen Biegun, who led pre-summit negotiations, met his Japanese and South Korean counterparts in Washington on Wednesday to discuss future steps, a State Department official said.

Mr Biegun and his South Korean counterpart, Special Representative Lee Do-hoon, shared a view that the current situation after the second US-North Korea summit would be very sensitive in advancing future talks between the two countries, Seoul's Foreign Ministry said yesterday.

But both envoys agreed to keep close consultation and discussed ways to resume US-North Korea talks at an early date, the ministry added.

After the bilateral meeting, Mr Lee and Mr Biegun had a working lunch joined by Japan's chief nuclear envoy Kenji Kanasugi, according to the ministry.

REUTERS, XINHUA