"Commercial satellite imagery from May 7 provided the first definitive evidence that dismantlement of the test site was already well underway," Efe news agency reported citing the 38 North website report that published and analysed satellite images of the site.
Pyongyang had announced it would publicly dismantle its Punggye-ri nuclear facility between May 23 and 25 by destroying the tunnels in the complex with explosions, blocking entrances and removing observation areas, research centres, and security structures.
According to the report, many key operational support buildings have been razed since their last analysis.
Some of the rails and mining carts used for excavation of the tunnels in the complex have also been dismantled and other small buildings have been removed.
During the summit, Pyongyang had pledged to work for a complete denuclearisation of the peninsula, having promised to stop its weapons tests earlier.
North Korea has carried out six underground nuclear tests--including the last and most powerful one in September 2017--at the Punggye-ri site.
A number of analysts have doubted North Korea's commitment to the denuclearisation, citing the example of 2008, when Pyongyang publicly dismantled parts of its uranium reprocessing plant but kept developing its nuclear programme.
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