"The President wants to make sure that we de-nuclearize the (Korean) peninsula", Sanders said.
United States officials asserted that a Trump-Kim meeting would hinge "on the basis that we see concrete and verifiable steps" with regard to North Korea's commitment to refrain from nuclear and missile testing.
While there was no reaction from Kim's regime, South Korean President Moon Jae-in said news of the summit - announced by his national security advisor on a visit to Washington - was "like a miracle".
No serving American president has ever met with a North Korean leader.
After months of high stakes inflammatory rhetoric with his North Korean counterpart, he has accepted an invitation to meet the man.
The two nations remain in a state of war because the 1950-53 Korean War ended with an armistice and not a peace treaty. And as Kim made eminently clear in his January 1st speech, he also seeks to "normalize" North Korea's nuclear status and, eventually, to gain acceptance of the North's nuclear weapons program, including from the United States. "I spoke to him very early this morning about that decision and we had a good conversation".
Mr. Trump doesn't do normal diplomacy, and this leap to a face-to-face meeting had his impulsive trademarks: spur of the moment in response to a Kim Jong Un offer relayed through South Korean mediators; no vetting with his senior advisers or as far as we can tell our Japanese allies; and no pre-planning. It's as simple as I hope our president is highly guarded when he's there.
"The United States has made zero concessions but North Korea has made some promises", Ms Sanders said, noting Pyongyang's promise to denuclearise and discontinue nuclear testing. George W. Bush rejected the idea even though the Pyongyang regime, under Kim Jong Il said it was ready to discuss giving up its nuclear arsenal. Here are some of the most notable things Trump and Kim have said about each other.
TRT World's Frank Ucciardo has more from NY. The 34-year-old North Korean leader has hit back with jibes, calling Mr Trump "a mentally deranged USA dotard".
But the comments were a sign that an end to a standoff between the two countries over North Korea's nuclear weapon program is not imminent.
He said that the North Korean leader has expressed his "commitment to denuclearisation" and will "refrain from any further nuclear or missile tests" during the negotiations.
Kim then called Trump a "lunatic and loser".
"Why would Kim Jong Un insult me by calling me 'old, ' when I would NEVER call him 'short and fat?' Oh well, I try so hard to be his friend - and maybe someday that will happen!" "It was a surprise to us that he was so forward-leaning", Tillerson said.
Trump has previously ridiculed Kim as "Little Rocket Man", slapping wideranging bilateral sanctions on the Pyongyang regime and also leading a drive for worldwide sanctions through the UN.
"This could really be the crowning achievement of the Trump administration".
The pair also "committed to maintain pressure and sanctions until North Korea takes tangible steps toward complete, verifiable, and irreversible denuclearization".