SINGAPORE - United States President Donald Trump expressed his gratitude on Monday (June 11) to Prime Minister Lee Hsien Loong for Singapore’s role in hosting the summit between the United States and North Korea, saying he appreciated the hospitality, professionalism and friendship.

"We have a very interesting meeting in particular tomorrow, and I think things can work out very nicely. But we appreciate your hospitality and professionalism and your friendship. Thank you very much," President Trump told Mr Lee as they began their working lunch at the Istana.

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The two leaders shared a warm handshake in front of cameras at 12.45pm before they sat down with their delegations.

Mr Lee and Mr Trump, who held a one-on-one meeting before the lunch, had a good discussion on a wide range of regional and global developments, according to Singapore's Ministry of Foreign Affairs (MFA).

An MFA statement said: "Both leaders reaffirmed the excellent relations between Singapore and the US across the economic, defence, and security spheres.

"President Trump thanked Prime Minister Lee for Singapore’s hosting of the US-Democratic People’s Republic of Korea (DPRK) Summit. President Trump also expressed the US’ continued commitment to engage the region and his support for Singapore’s chairmanship of Asean."

Mr Trump also accepted Singapore President Halimah Yacob's invitation to make a state visit to Singapore in November 2018, in conjunction with the 6th Asean-US Summit and 13th East Asia Summit, said the MFA.

Mr Lee and Mr Trump last met in October 2017, during the Singapore leader's official working visit to Washington at Mr Trump’s invitation.

Mr Trump, in his presidential state car nicknamed The Beast, arrived at the Istana before noon.

He was accompanied by a convoy of more than 30 vehicles from Shangri-La Hotel, where he is staying. Journalists and cameramen had been standing by around the hotel and the Istana for Mr Trump since about 10.30am.

Mr Trump's delegation includes the following:

Ms Stephanie Syptak-Ramnath, charge d'affaires of the US Embassy in Singapore; Mr Matthew Pottinger, senior director for Asian affairs of the US National Security Council (NSC); Mrs Sarah Huckabee Sanders, White House Press Secretary; Mr John Bolton, US National Security Adviser; Mr Mike Pompeo, US Secretary of State; Mr John Kelly, White House Chief of Staff; Mr Stephen Miller, senior adviser to the President for policy; Ms Mira Ricardel, Deputy National Security Adviser; Ms Sarah Tinsley, NSC senior director for strategic communications; Mr Peter Michael McKinley, US Ambassador to Brazil, and Ms Melissa Brown, Counsellor for Economic and Political Affairs at the US Embassy in Singapore.

Members of PM Lee's delegation include Deputy PM Tharman Shanmugaratnam, Law and Home Affairs Minister K. Shanmugam, Foreign Minister Vivian Balakrishnan, Communications and Information Minister S. Iswaran and Education Minister Ong Ye Kung.

Mr Ong posted a Facebook photo of Mr Trump, Mr Pompeo and Mr Kelly at the lunch. A copy of the menu was spotted in the photo.

The Straits Times understands that the lunch was catered by Gordon Grill at Goodwood Park Hotel. Dishes on the menu include angus beef tenderloin, lobster bisque and cherry jubilee with clotted ice cream.

During the meeting, the officials also celebrated Mr Trump's birthday. He is turning 72 on June 14.

Foreign Minister Vivian Balakrishnan posted a photo of Mr Trump posing with the birthday cake. "Celebrating birthday, a bit early," he wrote.

The US delegation left the Istana shortly after 2pm.

President @realDonaldTrump meeting with Prime Minister @leehsienloong of Singapore at the Istana Palace, ahead of tomorrow’s #TrumpKimSummit⁠ pic.twitter.com/sJv5pJbqIH — Dan Scavino Jr.🇺🇸 (@Scavino45) June 11, 2018

Mr Pompeo, in a statement after the working lunch, said Mr Trump and the entire US team are looking forward to Tuesday's summit with North Korean leader Kim Jong Un.

"We have had substantive and detailed meetings to date, including this morning with the North Koreans. The President is well-prepared for tomorrow’s engagement with Chairman Kim. The US position remains clear and unchanged.”

Mr Trump held a meet-and-greet session at Shangri-la Hotel after his engagement at the Istana. At about 2.15pm, he gave a 20-minute speech to about 200 to 250 servicemen, embassy staff and Americans working here, thanking the embassy staff for their preparations for the summit, according to some attendees at the closed session.

Mr Trump also described the lunch with his Singapore hosts as positive, and told the crowd he looked forward to the summit on Tuesday.

Said Mr Liam Gimon, an American who worked in Singapore as a criminal intelligence officer at Interpol for the past two years: "The president was very thankful for all the preparations Americans in Singapore - especially the embassy staff - has been putting in. He said he was also confident about the Summit with North Korea."

Added Ms Kartika Johnson, 45, who attended the event as a relative of a US embassy staff: "He made us feel appreciated."

Mr Trump landed at Paya Lebar Air Base just the night before, after attending the Group of Seven (G-7) summit in Canada. He retracted his endorsement of the major economic powers' joint communique while on his way to Singapore.

Meanwhile, diplomats from the US and North Korea met behind closed doors at The Ritz-Carlton, Millenia Singapore hotel, in a bid to narrow their differences ahead of the summit between Mr Trump and Mr Kim on Tuesday morning.

Former US special representative for North Korea policy Sung Kim, who has been leading the US in talks with North Korean Vice-Foreign Minister Choe Son Hui in the border truce village of Panmunjom since last month, is said to be continuing the discussions with his counterpart in Singapore.

Top of the agenda is Pyongyang's complete, verifiable and irreversible denuclearisation. Mr Kim is likely to ask for a security guarantee and the easing of sanctions in return, say analysts. A peace treaty ending the 1950-53 Korean War may also be on the table.

Before sitting down for talks on Tuesday, Mr Trump intends to meet one on one with Mr Kim, the White House said.

“We can expect a one-on-one at the beginning,” NSC spokesman Robert Palladino told reporters in Singapore on Monday.

Media reports earlier quoted sources as saying the two men will meet briefly, with just their interpreters but no aides in the room.

Mr Trump on Saturday said he believes he would know "within the first minute" of meeting Mr Kim if the North Korean leader is serious about surrendering his nuclear arsenal.

Top aides will join them for the formal talks later, and they will most likely include Mr Pompeo and Mr Bolton, as well as Mr Kim's sister, Ms Kim Yo Jong, and top aide and former spy chief Kim Yong Chol.

The summit is the first between a sitting US president and a North Korean leader, and comes after a year of tension on the Korean peninsula stoked by Mr Kim's numerous missile tests and a "maximum pressure" campaign led by the US to curb Pyongyang.