North Korean leader Kim Jong Un has made good on his promise to demolish his country’s nuclear test site, which was formally closed in a series of huge explosions as a group of foreign journalists looked on.

The explosions at the test site deep in the mountains of the North’s sparsely populated north east were supposed to build confidence ahead of a planned summit next month between Mr Kim and US President Donald Trump.

But Mr Trump cancelled the meeting on Thursday, citing “tremendous anger and open hostility” in a North Korean statement released earlier in the day.

The blasts were centred on three tunnels at the underground site and a number of buildings in the surrounding area.

North Korea held a closing ceremony afterwards, with officials from its nuclear arms programme in attendance.

The group of journalists witnessed the demolition, which touched off landslides near the tunnel entrances and sent up clouds of smoke and dust.

This May 7 2018 satellite image provided by DigitalGlobe shows the nuclear test site in Punggye-ri
This May 7 2018 satellite image provided by DigitalGlobe shows the nuclear test site in Punggye-ri (Satellite Image ©2018 DigitalGlobe, a Maxar company via AP)

North Korea’s state media called the closure of the site part of a process to build “a nuclear-free, peaceful world” and “global nuclear disarmament”.

“The dismantling of the nuclear test ground conducted with high-level transparency has clearly attested once again to the proactive and peace-loving efforts of the DPRK government being made for assuring peace and stability on the Korean Peninsula and over the world,” the North’s official news agency said.

North Korea’s formal name is the Democratic People’s Republic of Korea.

Mr Kim announced his plan to close the site, where North Korea has conducted all six of its underground nuclear tests, ahead of a summit with South Korea’s President Moon Jae-in in April and the planned summit with Mr Trump next month.

But even as North Korea made good on its gesture of detente, it lobbed a 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.

Mr Trump responded by cancelling the summit, saying in a letter to Mr Kim: “Sadly, based on the tremendous anger and open hostility displayed in your most recent statement, I feel it is inappropriate, at this time, to have this long-planned meeting.”

A copy of the letter sent to North Korean leader Kim Jong Un from President Donald Trump
A copy of the letter sent to North Korean leader Kim Jong Un from President Donald Trump (J David Ake/AP)

North Korea’s decision to close the Punggye-ri nuclear test site had generally been seen as a welcome gesture by Mr Kim to set a positive tone ahead of the summit.

In a statement earlier on Thursday, South Korea’s National Security Council called the closing the North’s “first measure towards complete denuclearisation”.

Not everyone was as optimistic, however.

The closing of the site is not an irreversible move and would need to be followed by many more significant measures to meet Mr Trump’s demand for real denuclearisation.

North Korea also did not invite international nuclear weapons inspectors, opting instead for the impact of the television footage to impress the world.

The first blast the visiting journalists witnessed came at around 11am local time after they made a 12-hour plus trip by train and convoy through the night and over bumpy dirt roads.

That explosion collapsed the complex’s north tunnel, which was used for five nuclear tests between 2009 and last year.

Two other explosions, at around 2.20pm and 4pm, collapsed the west and south tunnels, according to officials.

North Korea’s state media stressed that those two tunnels could have been used to carry out more tests at any time, countering reports that the Punggye-ri site had been rendered largely unusable after the six tests already conducted there.

Also blown up were observation posts and barracks used by guards and other workers at the facility.

A tunnel on the eastern side of the facility had already been shut down after an initial nuclear test in 2006.

North Korea said the demolition of the facility did not cause any leakage of radioactive materials or have any “adverse impact on the surrounding ecological environment”.

The journalists were allowed to stay at the site for about nine hours.