OSAKA, Japan — President Donald Trump made an extraordinary public offer Saturday to meet North Korean leader Kim Jong Un, inviting him to shake hands "and say hello" in the demilitarized zone between North and South Korea.

Trump issued the invitation to the North Korean leader on Twitter as he started his final day in Japan before flying to Seoul, where Trump planned to meet with the South Korean president.

"While there, if Chairman Kim of North Korea sees this, I would meet him at the Border/DMZ just to shake his hand and say Hello (?)!" the president tweeted.

The White House declined to comment about any potential meeting beyond the president's tweet.

If the meeting were to transpire, it would be the first time a U.S. and North Korean leader have met in the DMZ, which despite its name is the most heavily fortified border in the world. It would also mark the third face-to-face meeting between Kim Jong Un and Trump, who made history in 2018 as the first U.S. president to meet with a North Korean leader while in office.

Trump's last summit with Kim Jong Un — in Hanoi, Vietnam, in February — collapsed abruptly, with a planned signing ceremony scrapped and Trump explaining to reporters that "sometimes you have to walk." At the center of that failure, U.S. officials have said, was Kim's insistence that all nuclear sanctions be lifted in exchange for only some concessions sought by the U.S. from Pyongyang related to its nuclear program.

17 PHOTOS Donald Trump at the G20 summit See Gallery Donald Trump at the G20 summit President Donald Trump arrives to greet Japanese Prime Minister Shinzo Abe at the G-20 summit in Osaka, Japan, Friday, June 28, 2019. (AP Photo/Susan Walsh) Japan's Prime Minister Shinzo Abe shakes hands with U.S. President Donald Trump during the G20 summit in Osaka, Japan June 28, 2019. Sputnik/Mikhail Klimentyev/Kremlin via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. U.S. President Donald Trump speaks with Saudi Arabia's Crown Prince Mohammed bin Salman during family photo session with other leaders and attendees at the G20 leaders summit in Osaka, Japan, June 28, 2019. REUTERS/Kevin Lamarque U.S. Secretary of State Mike Pompeo and U.S. President Donald Trump look on during a bilateral meeting with Brazil's President Jair Bolsonaro at the G20 leaders summit in Osaka, Japan, June 28, 2019. REUTERS/Kevin Lamarque U.S. President Donald Trump looks on during a bilateral meeting with Brazil's President Jair Bolsonaro at the G20 leaders summit in Osaka, Japan, June 28, 2019. REUTERS/Kevin Lamarque Russia's President Vladimir Putin and U.S. President Donald Trump attend a meeting on the sidelines of the G20 summit in Osaka, Japan June 28, 2019. Sputnik/Mikhail Klimentyev/Kremlin via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. Russia's President Vladimir Putin and U.S. President Donald Trump the G20 summit in Osaka, Japan June 28, 2019. Sputnik/Mikhail Klimentyev/Kremlin via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. U.S. President Donald Trump, left, speaks to Britain's Prime Minister Theresa May prior to a working lunch at the Group of 20 (G-20) summit in Osaka, Japan, on Friday, June 28, 2019. Kiyoshi Ota/Pool via REUTERS Turkey's President Tayyip Erdogan and U.S. President Donald Trump walk off with fellow leaders after a family photo session at the G20 leaders summit in Osaka, Japan, June 28, 2019. REUTERS/Kevin Lamarque US President Donald Trump (L) is welcomed by Japanese Prime Minister Shinzo Abe prior to the family photo at the G20 Osaka Summit in Osaka on June 28, 2019. (Photo by Ludovic MARIN / POOL / AFP) (Photo credit should read LUDOVIC MARIN/AFP/Getty Images) French President Emmanuel Macron watches as President Donald Trump shakes hands with Japanese Prime Minister Shinzo Abe bbefore a working session at the G-20 summit in Osaka, Japan, Friday, June 28, 2019. (AP Photo/Susan Walsh) President Donald Trump, right, listens to a reporter's question during a bilateral meeting with Brazilian President Jair Bolsonaro on the sidelines of the G-20 summit in Osaka, Japan, Friday, June 28, 2019. Commerce Secretary Wilbur Ross, left, Treasury Secretary Steven Mnuchin, second from left, and Secretary of State Mike Pompeo, third from left, listen. (AP Photo/Susan Walsh) President Donald Trump, left, sitting next to Japanese Prime Minister Shinzo Abe, right, speaks during the G-20 summit event on the Digital Economy in Osaka, Japan, Friday, June 28, 2019. (AP Photo/Susan Walsh) President Donald Trump, left, shakes hands with Saudi Arabia's Crown Prince Mohammed bin Salman, as they gather for a group photo at the G-20 summit in Osaka, Japan, Friday, June 28, 2019. (AP Photo/Susan Walsh) President Donald Trump talks with Saudi Arabia's Crown Prince Mohammed bin Salman during a group photo at the G20 summit in Osaka, Japan, Friday, June 28, 2019. (AP Photo/Susan Walsh) President Donald Trump, right, meets with Russian President Vladimir Putin during a bilateral meeting on the sidelines of the G-20 summit in Osaka, Japan, Friday, June 28, 2019. (AP Photo/Susan Walsh) President Donald Trump speaks to European Commission president Jean-Claude Juncker during a session at the G-20 summit in Osaka, Japan, Friday, June 28, 2019. (AP Photo/Susan Walsh) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

In the run-up to Trump's trip to Japan for the Group of 20 summit and his subsequent stop in Seoul, there were signs that a potential tete-a-tete with Kim could be in the works. South Koreas president said publicly that U.S. and North Korean officials were holding "behind-the-scenes talks" to arrange a third summit between their leaders, although North Korea's foreign ministry later seemed to distance itself from that notion by saying that South Korea should cease trying to mediate with Washington.

It's unclear how much if any progress has been made between the U.S. and North Korea since the Hanoi summit in bridging the serious divides that led to its collapse. Still, the White House has acknowledged that Trump and Kim have continued to exchange correspondence since — messages that Trump has described as "beautiful letters" from the authoritarian leader of the nuclear-armed nation.

U.S. presidents and vice presidents occasionally visit the DMZ, a no-man's land that includes a designated area where North and South Korean officials periodically have met. High-level U.S. visits are typically shrouded in secrecy and accompanied by significant security arrangements, with American leaders often holding photo-ops from a vista where they can peer through binoculars at North Korean soldiers not far away.