North Korea 'rapidly' improving nuclear research facility, satellite images show

North Korea is making improvements to its main nuclear research facility, just weeks after declaring its commitment to denuclearisation.

Respected North Korea monitor 38 North has published satellite imagery that shows work on Yongbyon Nuclear Scientific Research Centre is continuing at a "rapid pace".

The images from 21 June showed several new buildings, including an engineering office and a driveway to a building which houses a nuclear reactor.

But they added: "Continued work at the Yongbyon facility should not be seen as having any relationship to North Korea's pledge to denuclearise.

"The North's nuclear cadre can be expected to proceed with business as usual until specific orders are issued from Pyongyang."

Captions for the satellite images noted that there was no vapour seen from the cooling tower and no visible steam plumes.

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Earlier in June, North Korean leader Kim Jong Un met Donald Trump in Singapore and promised to "work toward" the goal of denuclearisation.

The president hailed the agreement as "total denuclearisation, which is already taking place" but a timeline for the process had not been clearly defined.

In May, North Korea blew up its only nuclear test site at Punggye-ri, where it had staged six atomic tests.

Critics, however, said the site had been mostly unusable anyway.

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The satellite images were published as US Defence Secretary Jim Mattis and Chinese Defence Minister Wei Fenghe met to discuss how to get North Korea to fulfil the promise it made in Singapore.

While neither mentioned specific issues, it is expected North Korea is top of their agenda.