On Sunday, Bolton declined to comment on US intelligence assessments, but said the administration is "very well aware of North Korea's patterns of behavior over decades of negotiating with the United States".
The North Koreans may have made a public show of destroying a main nuclear weapons test site before the summit and halted nuclear and missile tests, but "there's no evidence that they are decreasing stockpiles, or that they have stopped their production", a USA official told NBC.
Japanese defense officials told the Asahi that Tokyo was following in the footsteps of the United States, which has already lowered its alert level in the Indo-Pacific region. But North Korean officials are suggesting that they declare far fewer.
Sunday's (July 1) report of his trip to Sinuiju, one of North Korea's earliest special economic zones, came a day after the state media reported his tour of a reed farm in the nearby Sindo county, also on the Sino-North Korea border.
"President Trump told us 'North Korea is no longer a nuclear threat, '" Murphy said.
Bolton dismissed a question about whether Trump has been more willing to criticise USA allies than authoritarian leaders of rival nations, including Putin and North Korea's Kim Jong-un.
White House national security adviser John Bolton. North Korea experts have rejected Trump's pronouncement, however, noting Pyongyang's long history of bad faith diplomacy and the fact that Trump was only able to obtain a vague mutual commitment to denuclearization from Kim.
TRUMP: I made a deal with him, I shook hands with him. Meeting with Kim Jong Un was an interesting and very positive experience.
US Stocks Open Higher on Bargain Hunting
Among the day's losers, the yuan weakened to 6.491 to the dollar in the offshore market, the lowest in five months. Beijing has mounted campaigns against Japanese and South Korean companies in the past after diplomatic disputes.
The officials insisted on anonymity to discuss sensitive assessments about a country that has always been one of the most hard targets for spy agencies to penetrate.
Bolton told CBS's Face the Nation that Washington has devised a programme to dismantle North Korea's weapons of mass destruction and ballistic missile programmes in a year.
As of now, there is little proof that North Korea intends to go down that road, longtime North Korea observers say.
One U.S. official said the regime has stopped nuclear and missile tests but "there's no evidence that they are decreasing stockpiles, or that they have stopped their production".
"I think they're very serious about it", the President responded.
The Washington Post reported on Saturday that USA intelligence officials have concluded that North Korea is unlikely to completely denuclearize and is preparing to hide parts of its nuclear weapons program during negotiations with the U.S.
At the same time, U.S. envoy Sung Kim held talks with North Korean officials on Sunday in the border village of Panmunjom within the demilitarised zone between the North and South Korea, South Korean media reported on Sunday.
US Secretary of State Mike Pompeo has acknowledged that it could take years to implement any agreement on eliminating North Korea's nuclear stockpile, a hard-won asset that North Korean leaders regard as a guarantor of their survival.
In recent years, the United States, through imagery and computer hacking, has improved its intelligence collection in North Korea.
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