Donald Trump and Kim Jong Un will likely meet again after New Year, the US vice president said, but insisted his government would not repeat past mistakes where "promises are broken."
The US president and the North's leader held a historic summit in Singapore earlier this year, signing a vaguely worded deal on denuclearisation.
North Korea has taken some steps since then -- forgoing nuclear and missile tests, dismantling a missile test site and promising to also break up the country's main nuclear complex if the US makes concessions.
But progress has generally been slow, with the two countries sparring over the exact meaning of the agreement.
Trump has said he hopes to have a second meeting with Kim early next year, but talks between Secretary of State Mike Pompeo and a top North Korean official planned for last week, partly to prepare for the meeting, were cancelled.
The US said the North axed the talks because they weren't ready, and Trump insisted he was in "no rush".
Speaking in Singapore, US Vice President Mike Pence insisted plans for the second meeting were still "ongoing".
"We believe that the summit will likely occur after the 1st of the year but the when and the where of that is still being worked out," he told reporters.
"We don't want to repeat the mistakes of prior administrations -- frankly both political parties have made over the last several decades -- where promises are made, sanctions are lifted and economic support comes and then promises are broken."
His comments came after a meeting with South Korean President Moon Jae-in on the sidelines of a summit attended by world leaders, including Russian President Vladimir Putin and Chinese Premier Li Keqiang.
- Maximum pressure -
Pence urged other countries at the meeting to keep up sanctions pressure on the North amid signs that Pyongyang's traditional trading partners, China and Russia, have eased enforcement.
Seoul has also said it is mulling lifting its own measures against Pyongyang.
US officials insist on the complete, verified and irreversible denuclearisation of the Korean peninsula before sanctions are lifted.
The North has rejected demands for what it calls "unilateral" disarmament, and has instead sought unspecified reciprocal US measures in a gradual process.
It has also called for sanctions to be eased as a reward for coming to the table, warning Washington's stance is undermining confidence.
Japanese Prime Minister Shinzo Abe piled on the pressure in a meeting with members of the 10-country Association of Southeast Asian Nations (ASEAN), insisting sanctions should be fully enforced.
"He urged ASEAN countries to collaborate on concrete measures such as ship to ship transfer of prohibited materials, including fuel," said foreign ministry spokesman Takeshi Osuga.
Trump has skipped this week's Singapore summit, the biggest annual meeting organised by ASEAN, raising new questions about US commitment to Asia.
Taking his place, Pence insisted America's commitment to the region was "steadfast and enduring".
"In all that we do the United States seeks collaboration not control," he said at the meeting with Southeast Asian leaders.
He also took a swipe at Beijing, whose growing assertiveness in the South China Sea has long been a source of friction with rival claimants in Southeast Asia and the United States.
"Empire and aggression have no place in the Indo-Pacific," Pence said.
"We stand shoulder-to-shoulder with you for freedom of navigation and our determination to ensure your nations are secure in their sovereign borders, on land and at sea."
Beijing claims almost the entire South China Sea, even areas approaching the coastlines of other countries, and has been establishing military installations on disputed outcrops.
After Singapore, Pence is heading to Papua New Guinea for a summit of the Asia-Pacific Economic Cooperation forum.