The destruction was undertaken in an attempt to reduce regional tensions.
At least three nuclear tunnels appear to have been destroyed at the Punggye-ri nuclear test site in North Korea on Thursday.
The information comes less than 24 hours after
Donald Trump called off his summit with Kim Jong-un.
In a latter addressed to North Korea, Trump said: "You talk about your nuclear capabilities, but ours are so massive and powerful that I pray to God they will never have to be used."
Tom Cheshire of Sky News was at the scene in Pnggye-ri and has since posted videos of the destruction of the tunnels on Twitter.
https://twitter.com/chesh/status/999935902884474880
https://twitter.com/chesh/status/999936625026138113
https://twitter.com/chesh/status/999937135909244928
And here's the aftermath...
https://twitter.com/chesh/status/999937840271253504