The left-leaning leader, whose diplomacy paved the way for historic summits between President Donald Trump and North Korean strongman Kim Jong Un, laid out his rosy vision for the last Cold War frontier in an address to the UN General Assembly.

He asked the international community to commit to designating the international peace area to replace the 250-kilometer (155-mile) Demilitarized Zone that has split the two Koreas for more than 60 years.

Moon said the zone would offer an added incentive for Kim to give up nuclear weapons, the focus of more than a year of on-again, off-again talks between North Korea and the United States.

"The establishment of an international peace zone will provide an institutional and realistic guarantee for North Korea's security," Moon said.

"At the same time South Korea will be able to gain permanent peace," he said.

Moon voiced hope that the zone, which is four kilometers wide, would become the home of UN agencies dedicated to conflict resolution and the environment and eventually be declared a world heritage site by UNESCO, the UN cultural body.

"It can become an international peace zone in name as well as substance," Moon said.

Despite the intense military buildups on each side of the Demilitarized Zone, "paradoxically it has become a pristine ecological treasure trove," he said.

"When the DMZ that cuts the midriff of the Korean peninsula is turned into a peace zone, the peninsula will evolve into a bridge nation that connects the continent and the ocean and facilitates peace and prosperity," he said.

He acknowledged steep challenges, including removing the estimated 380,000 mines in the Demilitarized Zone, but said that the peace proposal would boost demining efforts.

Moon said he had spoken to Kim about the restoration of Korea-wide railroads that have been severed since the 1950-53 war.

- Trump upbeat -

Despite Moon's optimism, North Korea has not taken concrete steps to end its nuclear program and has continued to fire short-range missiles, drawing particular concern in Japan.

Trump has nonetheless insisted that he likes Kim and trusts him, saying that the North Korean leader wrote him "beautiful" letters including for his birthday.

North Korea has called for a return to working-level talks with the United States by the end of the month, although no date has been announced.

In his own speech to the General Assembly, Trump called on North Korea to denuclearize but struck an upbeat tone hailing his own "bold diplomacy."

"America knows while anyone can make war, the only the most courageous can choose peace," he said.

Meeting on Monday with Moon, Trump told reporters that he was not considering additional pressure on North Korea.

"There's no reason for actions. I will say this: If I weren't president, you'd be at war with North Korea, in my opinion," he said.

UN Secretary-General Antonio Guterres, in his own speech to open the General Assembly, said he would welcome a new summit between Trump and Kim to address the "uncertain" situation on the Korean peninsula.