WASHINGTON, June 21 (Reuters) - U.S. President Donald Trump said on Thursday that North Korea was blowing up four of its big test sites and that a process of "total denuclearization ... has already started taking place."

Speaking at a meeting of his Cabinet at the White House, Trump said: "They’ve stopped the sending of missiles, including ballistic missiles. They’re destroying their engine site. They’re blowing it up. They’ve already blown up one of their big test sites, in fact, it’s actually four of their big test sites.

"And the big thing is it will be a total denuclearization, which has already started taking place."

RELATED: North Korea dismantles nuclear test site

21 PHOTOS North Korea dismantles nuclear test site See Gallery North Korea dismantles nuclear test site PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, taken on May 24, North Korea's Punggye-ri nuclear test site explosion on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by Handout/News1 via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, the entrance to a tunnel rigged with explosives is shown at North Korea's Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, a North Korean soldier stands at the entrance to a tunnel at the Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, taken on May 24, North Korea's Punggye-ri nuclear test site explosion on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by Handout/News1 via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, the debris is seen after demolition of the Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, North Korean soldiers stand at the entrance to a tunnel at the Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, taken on May 24, North Korea's Punggye-ri nuclear test site explosion on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by Handout/News1 via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, taken on May 24, North Korea's Punggye-ri nuclear test site explosion on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by Handout/News1 via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, a North Korean soldier stands at the entrance to a tunnel at the Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, a North Korean soldier stands at the entrance to a tunnel at the Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, taken on May 24, North Korea's Punggye-ri nuclear test site explosion on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, the entrance to a tunnel rigged with explosives is shown at the Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, members of the media make their way towards North Korea's Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, the debris is seen after a demolition 'ceremony' at the North Korea's Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, members of the media stand at the entrance to a tunnel prior to a demolition ceremony at North Korea's Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, the Punggye-ri nuclear test site is demolished on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, a North Korean soldier stands at the entrance to a tunnel at the Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, a North Korean soldier inspects debris before members of the foreign media following demolition of the Punggye-ri nuclear site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, the Punggye-ri nuclear test site is demolished on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, a North Korean soldier explains the demolition process of the Punggye-ri nuclear test facility to the media at the Punggye-ri nuclear test site on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) PUNGGYE-RI, NORTH KOREA - MAY 24: (SOUTH KOREA OUT) In this handout image provided by the News1-Dong-A Ilbo, North Korea's Punggye-ri nuclear test site is demolished on May 24, 2018 in Punggye-ri, North Korea. North Korea dismantled their nuclear testing facility at Punggye-ri in front of the international media. (Photo by News1-Dong-A Ilbo via Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Asked on Wednesday whether North Korea has done anything toward denuclearization since a landmark summit between Trump and North Korean leader Kim Jong Un on June 12, U.S. Defense Secretary Jim Mattis told reporters:

“No, I'm not aware of that. I mean, obviously, it's the very front end of a process. The detailed negotiations have not begun. I wouldn't expect that at this point.”

Mattis was sat next to Trump at Thursday's Cabinet meeting.

The U.S.-based North Korea monitoring group 38 North said in an analysis at the end of last week there had been no sign of any activity toward dismantling Sohae or any other missile test site.

(Reporting by Jim Oliphant, David Brunnstrom, Idrees Ali and Tim Ahmann in Washington Editing by James Dalgleish)

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