By Roberta Rampton

LA MALBAIE, Quebec (Reuters) - U.S. President Donald Trump said on Saturday any agreement with North Korean leader Kim Jong Un at next week's summit would be "spur of the moment," underscoring the uncertain outcome of what he called a "mission of peace."

"I have a clear objective, but I have to say - it's going to be something that will always be spur of the moment," Trump told reporters at a news conference at the G7 summit in Quebec. "You don't know. This has not been done before at this level."

The main issue for the June 12 summit in Singapore, which he departed for before the end of the G7 meeting, is the U.S. demand for North Korea to abandon a nuclear weapons program that now threatens the United States.

Trump said it would probably take time to reach an agreement with Kim on denuclearization, but at a minimum he believed the summit could produce a "relationship" between the United States and North Korea, which do not have diplomatic ties.

At a news conference with Japanese Prime Minister Shinzo Abe on Thursday, Trump said he might extend an invitation to Kim to visit Washington. Pyongyang has rejected giving up its arsenal unilaterally and defends its nuclear and missile programs as a deterrent against what it sees as U.S. aggression.

The United States stations 28,500 troops in South Korea, a legacy of the Korean War. Trump has held out the possibility of striking an accord with Kim that would formally end the 1950-53 Korean War, which was concluded with a truce, and not a peace treaty.

Trump on Saturday said he would know within a minute whether something good would come out of the summit.

"I think within the first minute I'll know. Just my touch, my feel. That's what I do," Trump said. "And if I think it won't happen - I'm not going to waste my time. I don't want to waste his time."

Trump frequently has boasted of his negotiating prowess as a real estate developer, and his ability to read people, even though his businesses have declared multiple bankruptcies.

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The U.S. leader was overall optimistic about the summit with Kim.

A rare direct flight from Pyongyang landed in Singapore on Saturday ahead of the expected arrival of Kim. The Air China Airbus 330 flight at Changi airport raised speculation that a delegation of North Korean officials joined an advance team headed by Kim's close aide, Kim Chang Son, who was in Singapore to prepare for the talks.

Kim is expected to arrive at Changi airport on Sunday, a source involved in the planning of the trip told Reuters on Friday.

(Reporting by Roberta Rampton; writing by Lucia Mutikani and Jonathan Landay; Editing by Susan Thomas)