Speaking just hours ahead of the historic meeting, the UN chief said experts from the International Atomic Energy Agency (IAEA) could help verify that North Korea has indeed scrapped its nuclear program, if the parties request their assistance.

"The world is closely watching what will take place in Singapore in a few hours' time," Guterres told reporters.

"The two leaders are seeking to break out of the dangerous cycle that created so much concern last year."

"Peace and verifiable denuclearization must remain the clear and shared goal," he added.

Donald Trump and Kim Jong Un are to discuss demands for Pyongyang to scrap its missile and nuclear programs during the meeting, the first ever between a sitting US president and a North Korean leader.

The United States is seeking complete, verifiable and irreversible dismantlement of Pyongyang's military programs - a process that would require experts on the ground to certify that North Korea is abiding by its commitments.

Guterres said "the road ahead will require cooperation, compromise and a common cause".

"There will be inevitable ups and downs, moments of disagreement and tough negotiations."

The UN chief called for donor contributions to a humanitarian appeal of $111 million to help six million North Koreans in need of aid and stressed the importance of improving respect for human rights in the communist-ruled country.

After North Korea last month invited foreign journalists to witness the closure of its Pungyye-ri nuclear test site, Guterres complained that international experts should have been there.