Modern relations with Vietnam are seen as a model for United States ties with the North.
He made public the summit venue in a Twitter message on Saturday (Seoul time) after Stephen Biegun, the U.S. envoy for North Korea, returned to South Korea following a trip to Pyongyang.
Both sides said they were committed to denuclearisation, but with no details of how this would be carried out or verified.
He ended his tweet: "I look forward to seeing Chairman Kim & advancing the cause of peace!"
Vietnam was reunited under Hanoi's control in 1975 after communist troops from the North captured the southern capital, then called Saigon and now known as Ho Chi Minh City.
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Après des coups d'éclat comme la quatrième place de Romain Grosjean en Autriche l'an passé, Haas va devoir confirmer avoir passé un palier.
Since the war, in which millions of civilians and combatants died, reunified Vietnam has rebuilt relations with America while remaining a communist state.
On his return to South Korea, Mr Biegun briefed the country's Foreign Minister Kang Kyung-wha.
Vietnam is also seen as a model of economic and political reform for the North to follow.
Critics fear the second summit is an attempt by Kim to win relief from USA sanctions without any real promise of denuclearisation.
What preparations are being made?
The two world leaders previously met in Singapore in June 2018.
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The two envoys will meet again ahead of the much anticipated summit at the end of the month.
Tokyo must work hard to persuade Trump that a complete disposal of all nuclear devices and missiles held by Pyongyang is vital for the peace and stability of Northeast Asia.
"The U.S. side has sounded out a foreign ministers' meeting".
Experts say tangible progress on Pyongyang's nuclear weapons will be needed for the second summit if it is to avoid being dismissed as "reality TV".
But tough sanctions have limited what they can do, with Washington insisting on keeping up economic pressure until North Korea takes stronger steps toward irreversibly and verifiably relinquishing its nuclear weapons.
"Following the Korean War, more than 100,000 divided Korean families came to the US Today, thousands of those families are still alive and hoping to reunite with their loved ones in North Korea", the group said.
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On last year's anniversary, North Korea staged a parade in Pyongyang at which it displayed what appeared to be intercontinental ballistic missiles such as its Hwasong-15, seen as capable of delivering a nuclear strike anywhere on the US mainland.