PUNGGYE-RI, North Korea (AP) — North Korea carried out what it said is the demolition of its nuclear test site Thursday, setting off a series of explosions over several hours in the presence of foreign journalists.

The explosions at the nuclear test site deep in the mountains of the North’s sparsely populated northeast were centered on three tunnels into the underground site and a number of observation towers in the surrounding area.

The planned closing was previously announced by leader Kim Jong Un ahead of his planned summit with U.S. President Donald Trump next month.

The demolition came as the North lobbed another verbal salvo at Washington, calling Vice President Mike Pence a “political dummy” and saying it is just as ready to meet in a nuclear confrontation as at the negotiating table.

The North’s decision to close the Punggye-ri nuclear test site has generally been seen as a welcome gesture by Kim to set a positive tone ahead of the summit. Even so, it is not an irreversible move and would need to be followed by many more significant measures to meet Trump’s demands for real denuclearization.

By bringing in the foreign media, mainly television networks, the North is apparently hoping to have images of the closing — including explosions to collapse tunnel entrances — broadcast around the world. The group included an Associated Press Television crew.

The North did not invite international inspectors to the ceremony, which limits its value as a serious concession.

The outburst at Pence, issued in the name of a top Foreign Ministry official, comes on the heels of another sharp rebuke of Trump’s newly appointed national security adviser, John Bolton, and has raised concerns that a major gap has opened between the two sides just weeks before the June 12 summit in Singapore.

In both cases, Pyongyang was trying to push back against hard-line comments suggesting North Korea may end up like Libya if it doesn’t move forward quickly and irreversibly with concrete measures to get rid of its nuclear weapons.

Choe Son Hui, a vice minister of foreign affairs, was quoted Thursday by the North’s state-run news agency slamming as “ignorant” and “stupid” comments Pence made in an interview with Fox News that compared the nuclear-capable North to Libya. Libya gave up its program at an early stage only to see its longtime dictator overthrown and brutally killed years later.

The summit plan has hit a number of speed bumps recently as both sides have begun trading barbs and taking tougher positions. Trump met with South Korean President Moon Jae-in on Tuesday at the White House for consultations and suggested the summit could be delayed or even called off entirely.

Even so, both sides still seem to want to hold the meeting, which would be unprecedented.

Success in talks would be a huge accomplishment for Trump. Meeting with the U.S. president as an equal on the world stage would be a major coup for Kim.