“It starts between our two countries,” so any discussion “would be premature as we wait for the outcome of the negotiations” in Singapore, Mattis added.

Asked whether North Korean military was on edge or showing unusual activity while its commander was in Singapore, Mattis said that “All’s quiet” on the peninsula.

Questions about troop levels arose after US officials repeatedly said the Trump administration isn’t pursuing regime change in North Korea and is willing to offer undefined security guarantees to Kim’s regime. Secretary of State Mike Pompeo reiterated that promise during a briefing with reporters in Singapore on Monday.

“We’re prepared to take actions that will provide them sufficient certainty that they can be comfortable that denuclearisation isn’t something that ends badly for them,” Pompeo said.

In Singapore on Monday night, North Korea and the United States projected optimism over the historic summit between their leaders, with the White House declaring last-minute preparatory talks a success, while a relaxed-looking Kim found time for a night tour of Singapore.

Kim’s big night out: North Korean leader goes sightseeing in Singapore

On the eve of his meeting with Trump, Kim spent more than two hours soaking in the city’s bright lights, viewing the panoramic skyline from the 57th floor of the Marina Bay Sands casino and hotel, and walking in the iconic Gardens by the Bay, a green lung in the downtown area. Talking to his hosts and smiling, he waved at the crowds jostling for pictures of him.

Trump made no such impromptu outings, but his staff nonetheless projected quiet confidence about the summit – the first ever between a sitting US president and North Korean leader.

The White House said in a statement that discussions between officials from both sides were “ongoing and have moved more quickly than expected” before the 9am meeting on Singapore’s Sentosa island.

Secretary of State Mike Pompeo meanwhile told reporters he was “very optimistic” about the summit, and insisted the US was willing to offer Pyongyang “unique” security guarantees if Kim’s government signed up for complete, verifiable, irreversible denuclearisation, or “CVID”.

His comments in the late afternoon dovetailed two rounds of talks between diplomats on both sides yesterday morning and in the afternoon to narrow down differences.

What’s on the table in Singapore? A birthday cake and denuclearisation

The US delegation was led by veteran diplomat Sung Kim, a South Korean by descent, while Pyongyang’s team was led by Choe Son-Hui, a vice-foreign minister.

Pompeo said the discussions earlier in the day moved “quite rapidly”.

Experts say the foremost issue that is probably being wrestled over was the US demand for CVID.

While the pressure is on for the talks to deliver concrete progress in this area, observers say this is a high bar unlikely to be achieved in just a few hours of talks.

The White House has said Trump will leave Singapore at 8pm tomorrow, about 11 hours after the summit begins. The two leaders will have a “one-on-one” meeting – accompanied by translators – before wider talks with their top aides.

They will then have a working lunch, according to a schedule of the meeting released by the White House. Kim is expected to leave Singapore soon after the lunch, sources told the Post.

Trump arrives in Singapore for historic summit with Kim Jong-un

A South Korean parliamentary source said negotiators from both countries “were debating over whether to put [the term] CVID” in the joint communique to be released after the summit.

“The two sides did not make much progress at Panmunjom a few weeks ago. But they did [on Monday],” the source said, forecasting that the Singapore summit is likely to be declared a “success”.

Boo Seung-chan, a research fellow at the Yonsei Institute for North Korean Studies in Seoul, was equally optimistic about the outcome.

“Trump and Kim both need a ‘gift’ to bring home,” Boo said. “North Korea will compromise [on having] a non-aggression agreement with the US. And the US at the same time will achieve the dismantlement of the North’s intercontinental ballistic missiles.”

Michael Kovrig, a senior adviser for northeast Asia at the International Crisis Group, said Pompeo’s comment that Trump “recognised Chairman Kim’s desire for security” signalled that the US may offer formal security guarantees to Pyongyang in exchange for nuclear disarmament.

Trump-Kim summit: North Korea wins first round 3-2

This may include the scaling back of US-South Korean joint military exercises, a written promise not to strike North Korea first and a commitment not to deploy nuclear-capable bombers and submarines around the Korean peninsula.

“Will that be enough? We don’t know. Kim might also want security assurances from China, Russia, and the United Nations Security Council,” Kovrig said.

Separately, UN Secretary General Antonio Guterres on Monday said the UN would assist both parties in the talks, including verifying North Korean denuclearisation, if asked.

“Relevant parts of the United Nations system stand ready to support this process in any way, including verification if requested by the key parties. They are the protagonists,” Guterres told reporters.

Denuclearisation on the schedule; Kim knows ‘world is watching’ him

The North Korean news agency KCNA said the meeting signalled “a changed era” in bilateral ties with Washington. It said the Singapore summit was being held “under the great attention and expectation of the whole world”.