USA and North Korean officials have held several meetings to discuss the return of the remains, with some media reporting the first batch will be delivered Friday.
According to 38 North, the group that monitors North Korea, images taken from Friday showed work has been carried out at a building where space launch vehicles are assembled and at a nearby engine test stand used to develop liquid-fuel engines for ballistic missiles and space launch vehicles.
The factory visit was the latest of a series of site inspections by Kim, including industrial facilities and special economic zones near North Korea's border with China, according to state media, after Kim shifted his focus from nuclear missiles to the economy in April.
"We had a fantastic meeting with Chairman Kim and it seems to be going very well", Trump added, referring to his summit last month with North Korean leader Kim Jong Un.
An official with knowledge of North Korea's position on the matter told CNN that Pyongyang may abandon talks on denuclearization if the USA does not agree to such a deal.
South Korean officials have also said they detected dismantlement activities at the site, though didn't specify the exact nature of the activities.
The 38 North report comes amid growing questions about North Korea's willingness to live up to the commitments Kim made at the June summit, particularly to work toward denuclearization. The leaders concluded their summit by declaring their vague aspirational goal of moving toward a nuclear-free Korean Peninsula, but there's lingering doubts on whether Kim would ever agree to fully give up the nuclear weapons that he may see as a stronger guarantee of his survival than whatever security assurances the United States can provide. "This could (and that is a big could) mean that North Korea is also willing to forgo satellite launches for the time being as well as nuclear and missile tests".
"Verification is obviously something that is paramount", she said at a regular press briefing.
Seoul's presidential office said Tuesday that it has been briefed on the movements and that it will have a positive impact on denuclearization.
The launching station is believed to be the one North Korea promised U.S. President Donald Trump it would take down during their summit in Singapore.
Real progress, Keane said, would include North Korea complying with previous knowledge from USA intelligence services.
It said they should "implement effective due diligence policies, procedures, and internal controls to ensure compliance with applicable legal requirements across their entire supply chains".
In a tweet early on Monday, Mr Trump rejected "fake news" that he was angry because progress was not happening fast enough with North Korea.
On June 20, Trump erroneously said 200 human remains had already "been sent back" from North Korea, but the issue is far from resolved and Pyongyang has already cancelled at least one meeting to discuss the return of the remains.
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