Osaka, Japan (CNN) President Donald Trump extended what he claimed was a spontaneous invitation to North Korean dictator Kim Jong Un for a handshake on the highly fortified Korean Demilitarized Zone, lending his upcoming visit to Seoul new drama.

In a Saturday morning tweet from his hotel in Japan, Trump said if Kim was interested he'd be open to a greeting on the border.

"If Chairman Kim of North Korea sees this, I would meet him at the Border/DMZ just to shake his hand and say Hello(?)!" Trump wrote.

Trump is due to arrive in Seoul, South Korea, on Saturday evening, and is scheduled for talks with the South Korean President on Sunday before returning to Washington.

A senior US official helping to plan the President's visit to the DMZ told CNN that key officials involved in the planning learned of the possible Trump-Kim DMZ handshake all at the same time -- from Trump's tweet suggesting the idea.

During a brief photo-op with reporters Saturday, Trump said he "put out a feeler" to Kim for a potential handshake on the DMZ in order to advance their warm friendship.

"All I did was put out a feeler if he'd like to meet," Trump told reporters in Japan, where he is meeting with leaders on the sidelines of the G20. "He sent me a very beautiful birthday card."

Trump told reporters later Saturday that Kim was "very receptive to meeting."

"I can't tell you exactly but they did respond very favorably," Trump said of the possibility of a meeting.

Trump also told reporters he would feel "very comfortable" stepping foot in North Korea when he visits the DMZ Sunday.

"Sure I would," Trump said when asked whether he would step foot into the country.

"I feel very comfortable doing that. I would have no problem," Trump said in Osaka.

No sitting US president has ever visited North Korea, though former presidents Jimmy Carter and Bill Clinton have made the trip.

Trump also insisted it would not be a bad sign if Kim stands him up.

"No, of course I thought of that," Trump said when asked if it should be interpreted as a bad sign if Kim failed to meet him.

"It's very hard," he said of the US-North Korea situation, noting that Kim "follows my Twitter."

Asked if he knew that to be a fact, Trump said his team "got a call very quickly" after his tweet.

Dramatic history

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The invitation carried some of the hallmarks of Trump's past meetings with Kim, namely the heightened drama and spectacle over whether the meeting would take place. But those meetings were planned well in advance, preceded by lower-level talks between US and North Korean officials.

This session appears more ad-hoc, at least in Trump's telling. He said he wasn't sure whether the meeting would materialize, but expressed confidence his diplomatic opening with North Korea was already yielding results.

"I just put out a feeler because I don't know where he is right now. He may not be in North Korea," Trump said. "I said if Chairman Kim would want to meet, I'll be at the border. We seem to get along really well. That's a good thing, not a bad thing. For the stupid people who say, 'Oh, he gets along,' it's good get along."

"Frankly, if I didn't become president, you'd be having a war right now with North Korea," Trump said.

"I will be in South Korea. I let him know, and we'll see. We'll see each other for two minutes. That's all we can. But that will be fine," Trump said.

North Korea responded to Trump's invitation through their first vice minister of foreign affairs in a statement on North Korean state media KCNA.

"We see it as a very interesting suggestion, but we have not received an official proposal in this regard," the minister, Choe Son Hui, said.

A meeting "would serve as another meaningful occasion in further deepening the personal relations between the two leaders and advancing the bilateral relations," the statement read.

Last week, a South Korea official said the President was considering a visit to the DMZ . He last attempted to visit the border zone during a visit to Seoul in 2017, but plans were scrapped due to heavy fog.

If he goes, he'll follow in the footsteps of his most recent predecessors, who journeyed to the border zone to peer into North Korea through binoculars.

Trump's last summit meeting with Kim collapsed when the two sides could not agree on terms for curbing North Korea's nuclear program in exchange for sanctions relief.

Since then, talks have been sporadic between Washington and Pyongyang. But there have been glimmers of progress in a letter exchange between Kim and Trump, including birthday greetings for the US President earlier this month.

This story has been updated.