North Korea said Thursday it has "completely" dismantled its only known nuclear test site in Punggye-ri in the presence of foreign reporters as promised, hours before U.S. President Donald Trump abruptly called off next month's planned Washington-Pyongyang summit.

It said in a statement that the demolition was conducted in such a manner as to "make all the tunnels of the test ground collapse by explosion and completely close the tunnel entrances."

(Punggye-ri Nuclear test site)
[Google Earth/38 North]

The foreign journalists who visited the Punggye-ri test site in the country's northeast reported that three underground tunnels, observation buildings and other facilities used for nuclear testing were blown up.

The reporters said they witnessed the explosions from observation decks about 500 meters away.

"There was a huge explosion, you could feel it. Dust came at you, the heat came at you. It was extremely loud," a reporter from Britain's Sky News said.

One of the three tunnels was demolished at 11 a.m. and the other two were done about 2 p.m., they said, adding that the explosions, carried out over several hours, ended after 4 p.m.

"There were neither leakage of radioactive materials nor any adverse impact on the surrounding ecological environment," the North's Nuclear Weapons Institute, which released the statement, said.

"The discontinuance of the nuclear test is an important process moving toward global nuclear disarmament," the statement carried by the country's official Korean Central News Agency said.

It said the area around the test site will totally be closed after all ground observation facilities, research institutes, structures of guard units and staff are removed.

Pyongyang had earlier said it would hold a ceremony to mark the closure between Wednesday and Friday, depending on weather conditions, as a key step toward denuclearization on the Korean Peninsula.

(Kim Jong un, center right, at a facility thought to be linked to the North's nuclear development)
[File photo, KNS/Kyodo]

The explosions were observed by about a total of 30 invited reporters from Britain, China, South Korea, Russia and the United States.

Punggye-ri is where North Korea has conducted all six of its nuclear weapon tests to date, beginning in 2006, including the most powerful one last September.

Trump and North Korean leader Kim Jong Un had earlier planned to meet on June 12 in Singapore.

North Korea allowing the foreign journalists to conduct on-the-spot coverage of the demolition was seen as a sign of goodwill from Kim, but there was skepticism that the event might be only a "political show."

Experts such as those from the International Atomic Energy Agency were not invited to observe the dismantling, raising concern that the actual condition of the test site after demolition will not be revealed.

At his summit with South Korean President Moon Jae In on April 27, Kim pledged to shut down the nuclear test site in May and disclose its dismantlement to foreign experts and media to ensure transparency.

At a plenary meeting of the Central Committee of the Worker's Party of Korea last month, North Korea decided to dismantle the test site, as well as suspend nuclear and missile tests.

"The mission of the northern nuclear test ground has thus come to an end," Kim, chairman of the ruling party, was quoted as saying by KCNA.

Kim was believed to have started to commit "complete" denuclearization on the divided peninsula to gain security guarantees and other returns from Washington.

Trump, however, canceled on Thursday the summit with Kim, criticizing recent hostile remarks by North Korea.

(Kim Jong Un in a meeting with South Korean Pres. Moon Jae In on April 27)
[Korea Summit Press Pool]

Experts such as those from the International Atomic Energy Agency were not invited to observe the dismantling, raising concern that the actual condition of the test site after demolition will not be revealed.

At his summit with South Korean President Moon Jae In on April 27, Kim promised to shut down the test site in May and disclose its closure to foreign experts and media to ensure transparency.