North Korea on Thursday blew up tunnels dug beneath Mount Mantap at the Punggye-ri nuclear testing site in the northeastern region of the country, where all six of North Korea’s nuclear tests were conducted.

The site destruction began at 11 a.m. local time, and a small group of international media were present to witness the demolition of the tunnels, Reuters reported.

After five hours, three tunnels, two military barracks, and other facilities used for nuclear testing were destroyed, according to South Korean media.

The destruction of this site comes before a planned meeting between North Korean leader Kim Jong Un and President Trump in Singapore June 12 to discuss denuclearization of the Korean Peninsula.

North Korea’s offer to demolish the testing site is seen as a move towards easing tensions. But in recent weeks, Pyongyang has threatened to pull out of the summit following joint military demonstrations between the U.S. and South Korea.