Former US President Donald Trump said in a soon-to-be-published book that his summitry with North Korean leader Kim Jong-un during his time in office showed "real change" was "indeed" possible, portraying it as "honest, direct and productive."

The Republican presidential candidate made the remarks in the photo book, titled "Save America," reinforcing speculation that should he win the Nov. 5 general election, he could revive his personal diplomacy with the recalcitrant leader in Pyongyang.

He also took stock of his engagement with South Korea during his White House term from 2017-2021, saying he forged a "great" relationship with the Asian ally though he pointed out having Seoul start "paying more" for defense was "very important" to him.

"Chairman Kim Jong-un has an opportunity like no other -- to be remembered as the leader who ushered in a glorious new era of security and prosperity for his people," he wrote in the book, set to be released Tuesday.

"Our unprecedented meeting, the first between an American president and leader of North Korea, proves that real change is indeed possible. My meeting with Chairman Kim was honest, direct and productive. We got to know each other well in a very confined period of time," he added.

During his presidency, Trump pushed for an unconventional leader-to-leader approach toward North Korea, leading to three in-person meetings with Kim, including the first-ever summit between the United States and the North in Singapore in June 2018. But nuclear diplomacy stalled after the summit in Hanoi ended without a deal.

Among the photos related to the North was one showing Trump briefly crossing the Military Demarcation Line into the North on foot and becoming the first sitting US president to do so during his visit to the inter-Korean border truce village of Panmunjom in June 2019.

During a campaign rally in Pennsylvania on Friday, Trump boasted about the crossing of the inter-Korean border, casting him as the "first person to ever walk over from this country" and claiming that "getting along" with Kim is a "good thing."

The book also carried a photo of Trump, former President Moon Jae-in, and first ladies Melania Trump and Kim Jung-sook posing for a photo during Trump's visit to the then presidential office of Cheong Wa Dae in Seoul in November 2017.

"Moon Jae-in, president of South Korea -- I developed a great relationship with South Korea, even though it was very important to me that they start paying more money for defense," Trump wrote.

During his presidency, Trump demanded a hefty increase in Seoul's financial contributions to stationing the 28,500-strong US Forces Korea, raising questions over what was seen as his "transactional approach" to regional allies and causing friction in the Seoul-Washington relationship.

The release of the book comes as Trump and Vice President Kamala Harris are in a tight race for the White House with this week's Labor Day signaling the final stretch of their campaigns.

Trump took a jab at Harris, tripling down on his criticism of the Biden administration's policy on border security.

"Kamala Harris, the border czar, was a disaster! She had no idea what she was doing and never went to the border. That is what will happen to our country -- same thing, bigger scale!" he said.

"It happened under her watch in San Francisco, also. We won't let this happen to the USA. Make America Great Again!"

The book also carried photos of the assassination attempt in Pennsylvania in July. He recounted that he survived it and shouted to the crowd, "Fight, fight, fight."

"There was blood pouring everywhere, and yet, in a certain way, I felt very safe, because I had God on my side," he said. (Yonhap)