SINGAPORE, U.S. and North Korean officials held marathon talks on Monday to finalize details of a nuclear agreement ahead of their leaders' summit the following day.

Ambassador Sung Kim, the State Department's top Korea expert, met Choe Son-hui, the North's vice foreign minister, at the Ritz Carlton hotel for negotiations on what will be included in the summit agreement.

U.S. President Donald Trump and North Korean leader Kim Jong-un are set to hold their historic meeting at the Capella Hotel on Singapore's Sentosa Island on Tuesday, with the communist state's denuclearization topping the agenda.

The working-level talks resumed late at night after the two sides left the hotel earlier in the day following less than five hours of negotiations.

U.S. Secretary of State Mike Pompeo said earlier in the day that U.S. and North Korean officials held "substantive" talks.

"Substantive and detailed meetings in #Singapore today as Ambassador Kim meets with #DPRK @StateDept," Pompeo tweeted, together with photos of the officials in talks.

Choe and Kim already had several rounds of discussions at Panmunjom on the inter-Korean border that were reportedly focused on summit agenda items, including denuclearization and security assurance measures.

The working-level consultations are apparently aimed at making 11th-hour progress ahead of the summit since previous talks failed to narrow their differences over denuclearization methods and timetables.

The North's leader arrived in Singapore on Sunday, his first-known trip outside Northeast Asia since taking power in 2011.

Shortly afterward, he had a meeting with Singapore's Prime Minister Lee Hsien Loong at the Istana palace, during which he expressed gratitude for providing logistical support for the summit.

Kim was also quoted as saying that, "If the summit produces positive outcomes, then the Singaporean government's effort will be recorded in history forever."

On Monday morning, the North's state-controlled media broke their silence on his overseas trip.

The Korean Central News Agency said issues of mutual concern, related to the "changed era," will be on the agenda at the summit, including bilateral relations, peace and denuclearization.

Trump also flew into Singapore on Sunday, shortly after attending the Group of 7 summit in Canada. On Monday, he held talks with the Singaporean prime minister at the Istana.

"Great to be in Singapore, excitement in the air!" he tweeted ahead of the meeting.

Speaking to reporters in Canada, Trump called his talks with Kim a "one-time shot" for the North's young ruler.

"I feel that Kim Jong-un wants to do something great for his people," he said. "And he has that opportunity, and he won't have that opportunity again."

They plan to start the first-ever face-to-face meeting between the leaders of the Korean War foes at Sentosa's Capella Hotel at 9 a.m. Tuesday.

Source: Yonhap News Agency