Bolton's comments come only days after Trump himself said that he's a "little disappointed" by reports of new activity at a North Korean missile research center and long-range rocket site and that time will tell if US diplomacy with the reclusive country will be successful. "He's invested a lot of time in trying to develop that relationship", Bolton told ABC's "This Week".
Since 2017, North Korea has frozen nuclear and missile testing.
"Stay away, or a different vote is counted as a betrayal", writes the North Korean refugees-organized web site "Daily NK" in South Korea.
Trump said Kim promised he would carry out no more missile or nuclear testing, adding, "I take him at his word".
John Bolton has said that President Donald Trump was open to a third summit with North Korean leader Kim Jong-un, although nothing has been scheduled. I'll just put it this way - spends a lot of resources and efforts so we don't have to rely on commercial satellite imagery.
The Trump administration and many US lawmakers across party lines still believe in a hard-line stance on North Korea, maintaining that there can be no sanctions relief before denuclearization, according to multiple diplomatic sources Thursday.
Chance The Rapper weds childhood friend
The wedding comes less than a year since Chance got down on one knee on Fourth of July and popped the big question. Added the eyewitness: "After the ceremony, Kim and Kanye hung out with Dave Chappelle on the lawn".
"We see exactly what they are doing", he said.
Speaking at a conference organized by the Carnegie Endowment for International Peace, Biegun said progress had been made despite the failure of Trump's second summit with North Korean leader Kim Jong Un, held in Hanoi last month.
Amid an improvement in ties between Pyongyang and Seoul, the two sides are keen in resuming inter-Korean economic cooperation that had stalled in recent years due to sanctions against the DRPK.
Trump and Kim first met in Singapore in June 2018, producing only a North Korean commitment to "work towards complete denuclearization of the Korean peninsula".
South Korea's military said it is carefully monitoring North Korean nuclear and missile facilities after the country's spy agency told lawmakers that new activity was detected at a research center where the North is believed to build long-range missiles targeting the US mainland.
Bolton told ABC that he was not aware of any contact between the U.S. and North Korea since Vietnam, though it was "possible the South Koreans have spoken to North Korea".