North Korea is carrying out 'rapid improvements' to its main nuclear research facility, despite Kim Jong Un's promise to commit to denuclearisation of the peninsula during his summit with Donald Trump earlier this month.

New satellite images show that not only are operations continuing at the Yongbyon nuclear site, several new buildings have been erected in recent months, monitoring website 38 North said today.

At the end of the Singapore talks, Kim said he would 'work toward' the goal, but neither he nor Trump defined denuclearisation or set a deadline.

Mystery: There is no visible steam is being vented from the 5MWe (megawatt electrical) reactor to confirm that it is in operation, but 38 North said it could just be due to 'insufficient image resolution', and the image shows a new cooling water pump house bottom right

Cool river: A newly in-filled water channel is seen leading up to the new cooling water pump house from the river

Making moves: The images from 38 North show a new engineering office building, complete with a new concrete driveway, at the Experimental Light Water Reactor, as well as a small blue building nearby with unknown purpose

Trump claimed the process would start quickly, saying last week that 'It will be a total denuclearisation, which is already taking place.'

But the new satellite images does not show any slowing down of the continued development of Kim's main nuclear site, according to 38 North.

'Commercial satellite imagery from June 21 indicates that improvements to the infrastructure at... Yongbyon Nuclear Scientific Research Center are continuing at a rapid pace,' it said.

It noted 'continued operations' at the North's uranium enrichment plant and several new installations at the site - including an engineering office and a driveway to a building housing a nuclear reactor.

But continued operations at the site 'should not be seen as having any relationship with North Korea's pledge to denuclearise', it added.

Sticking to his word? Despite promising Donald Trump to 'work toward' denuclearisation at the Singapore summit, Kim Jong Un is keeping staff busy at his nuclear site

Previous satellite images had shown only the foundation where there is now a small blue building, which appears 'identical in size and design' to the blue structure near the Experimental Light Water Reactor

Getting richer: This satellite image shows increased roof staining at the Uranium Enrichment Plant, indicating that it is kept in operation

Two new buildings have appeared at what is presumed to be a radioisotope production facility, which could be used to store chemicals

Nuclear officials could be 'expected to proceed with business as usual until specific orders are issued from Pyongyang', it said.

The North last month blew up its aged but only nuclear test site at Punggye-ri - where it had staged six atomic tests - in a show of goodwill before the summit.

But Pyongyang has kept its counsel on the denuclearisation issue since the meeting, although state media have dialled down propaganda against the US, long dubbed the 'imperialist enemy.'

US Secretary of State Mike Pompeo has been pushing for more follow-up talks to flesh out details over denuclearisation but no date has been set for when they would take place.