The images show five specialised railcars near its Uranium Enrichment Facility and Radiochemistry Laboratory (Picture: CSIS/Digital Globe 2019/Beyond Parallel).
Satellite images have emerged showing movement at North Korea's main nuclear site, which could be associated with the reprocessing of radioactive material into bomb fuel, according to a US think tank.
The images, taken on 12 April from Yongbyon nuclear site, show five specialised railcars near its Uranium Enrichment Facility and Radiochemistry Laboratory.
Previously, these specialised railcars were associated with the movement of radioactive material or reprocessing campaigns, according to a report by 'Beyond Parallel'.
The report added:
"The current activity, along with their configurations, does not rule out their possible involvement in such activity, either before or after a reprocessing campaign."
If North Korea is reprocessing activity at any of its nuclear sites, it would undermine the ongoing talks with the US, where US President Donald Trump has been striving for the North Korean leader to denuclearise its sites.
Both leaders have met twice in the past year - with Donald Trump trying to persuade Kim Jon Un to abandon a nuclear weapons program that threatens the United States.
But there has been little progress.
The last summit between the two leaders, in February, ended without a deal, with Mr Kim later speaking out saying the US needs to be more flexible.
However, last week, Mr Kim has said he would be happy to meet Mr Trump again for a third summit, but only if the US came with the right attitude.
He said he would "wait til the end of the year" for the US to decide to be more flexible.
Mr Trump said he would also like to meet with the North Korean leader, adding the fact that their "personal relationship remains very good".
Experts have estimated the size of North Korea’s nuclear arsenal at anywhere between 20 and 60 warheads.