North Korea spent the whole of winter enriching uranium, though the aim remains unclear.
The country’s main nuclear complex showed continued activity, according to a US monitor.
Satellite imagery of its uranium enrichment facility showed movement of specialised vehicles and equipment nearby in January and February this year.
This suggests the Uranium Enrichment Plant (UEP) has continued operations, reports Yonhap.
However, experts analysing satellite imagery said there were no signs of activity at nuclear reactors.
The US monitor website said: “In contrast to the reactor area of the complex, the UEP exhibited continual signs of operation throughout the winter months.”
Images showed “uniquely configured, specialised railcars” arriving and departing the facility.
Previously, these railcars arrived two to three times a year, possibly transferring chemical reagents, says the outlet.
Earlier this month it was reported North Korea poses a new “catastrophic threat” to the world in 2021, experts have warned.
Foreign policy wonks claim a fresh emergency caused by the rogue state is of major concern in 2021.
The Council on Foreign Relations (CFR) has laid out the stark danger from Kim Jong-un’s regime and its nuclear capabilities.
Its annual preventive priorities survey ranked a crisis stemming from its continued development of nuclear weapons and ballistic missile testing as the “top-ranked conflict concern for 2021”.
And it means North Korea’s nuclear programme is now a bigger threat than a cyberattack on US critical infrastructure, which was the top concern in 2019 and 2020.
Tubby tyrant Kim Jong-un tends to use nuclear and missile tests to taunt new world leaders, raising fears more could be on the way now that Joe Biden has been sworn in as President.
Last month, Jong-un declared the US was North Korea’s “foremost principal enemy” at a meeting of the Worker’s Party of Korea, news.com.au reports.
The dictator blasted America’s “hostile policy” towards the hermit kingdom.