North Korea has reportedly started pulling cables from tunnels at its Punggye-ri nuclear test site, a first step toward closing them down. 

U.S. broadcaster CBS News issued the report on Wednesday quoting U.S. intelligence, but did not elaborate further details. 

The reported move came after North Korean leader Kim Jong-un vowed to shut down the country's nuclear test site in May during his summit with President Moon Jae-in at the Panmunjeom border truce village last week. 

Kim later announced that he would invite experts and journalists from South Korea and the United States to reveal the process to the outside world. 

The Punggye-ri site is known as the North's main nuclear facility. All six of the North's nuclear tests since October 2006 have been conducted there.