They are "finalising preparations and will remain in place until the summit begins", said Sanders.
When asked if the US would allow a third party to pay for parts of the summit, a White House official said the "United States government will pay its own expenses" but did not rule out an outside contribution on North Korea's behalf.
Experts have voiced concern that despite Trump's claim to be the world's greatest dealmaker, he knows little about North Korea, arms control or global diplomacy.
"A summit is not a strategy, and a summit without a strategy is risky", warned Cha, who in January was withdrawn from consideration to be a USA ambassador apparently after he disagreed with White House interest in a limited strike against North Korea.
In September a year ago, Kim described Trump as a "mentally deranged United States dotard".
The White House this week confirmed the summit between Trump and Kim would be held on Singapore's southern island of Sentosa.
"Through these series of meetings, I'm confident we're moving in the right direction.It could be nothing short of tragic to let this opportunity go to waste", Pompeo said.
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"I think what Mr. Abe expects is [that Trump] will at least raise this issue with Kim Jong-un when they meet", said Tetsuo Kotani, a senior fellow at the Japan Institute of International Affairs.
While the summit getting back on track has fueled hopes for concrete results between Pyongyang and Washington, denuclearizing North Korea appears likely to become drawn out and involve political processes within the US. "But the relationships are building, and that's a very positive thing". The Shangri-La hotel had always been seen as the likely venue for the summit and had previously hosted former US presidents George H.W. Bush and Barack Obama.
In the past, 56-year-old Rodman has praised Trump for the planned summit, saying it was "a historical meeting no US president has ever done".
On Monday, the hotel was blocked from public access and was not taking reservations for June 12, according to South Korean news agency Yonhap.
Trump, Kim and their delegations are likely to enter Sentosa by vehicle via the causeway.
The move imposes restrictions to certain activities within the delineated areas.
On Wednesday, following the announcement of the venue, the Singapore government declared the Trump-Kim summit an "Enhanced Security Special Event", under which it will enforce strict security measures at the venues and surrounding areas through spot checks and inspections. The rule remains in effect from June 3 to 30, weeks after the summit concludes.