"Possible progress being made in talks with North Korea," Trump tweeted in his first response to the overture. "For the first time in many years, a serious effort is being made by all parties concerned."

"The World is watching and waiting! May be false hope, but the U.S. is ready to go hard in either direction!"

South Korea's national security advisor Chung Eui-yong announced the potential breakthrough in Seoul after returning from a meeting with North Korean leader Kim Jong Un, in which the two sides agreed to hold a summit next month in the Demilitarized Zone.

Chung said the North is open to "frank" talks with the United States on denuclearization and would suspend missile and nuclear tests while dialogue was under way.

It is willing to abandon the programs if its national security -- and that of its leadership -- is guaranteed, Chung said.