U.S. President Donald Trump has said a process of North Korea's "total denuclearization" has already started and the North has destroyed four of its big test sites. 

Speaking at a Cabinet meeting at the White House on Thursday, Trump said that the "number-one statement" in the document he and North Korean leader Kim Jong-un signed in Singapore was that the North will begin total denuclearization right away. 

The president also said that North Koreans are destroying their engine site and they've already blown up one of their big test sites, adding that in fact, it was actually four of their big test sites. 

It remains unclear which test sites Trump was referring to. In May, North Korea destroyed its only known nuclear test site, Punggye-ri, which included four testing tunnels.

[Photo : YONHAP News]