North Korea has been preparing to make nuclear missiles throughout the winter as Kim Jong-un continues to taunt the West, it has been claimed.
It is believed uranium is continuing to be prepped at the Hermit Kingdom's main enrichment plant, with satellite images showing increased activity, according to US monitors.
It comes just weeks after the Council on Foreign Relations (CFR) identified Kim's focus on nuclear weapons as the biggest threat to the world.
Referring to the new imagery, American monitoring website 38North said: "In contrast to the reactor area of the complex, the UEP exhibited continual signs of operation throughout the winter months.
"Most notable is the arrival and departure of three uniquely-configured, specialized railcars.
"These railcars follow a pattern: arriving two to three times a year at the rail transfer station...where they stay for approximately four weeks as they transfer their content, probably chemical reagents, and then depart."
Pyongyang is under international sanctions for its nuclear weapons and ballistic missile programmes.
US President Joe Biden's administration is understood to be planning a full review of its approach to North Korea in order to re-start talks over sanctions and potential aid.
However, it is believed Kim is using any opportunities of negotiating with America to advance rather than decelerate his nuclear arms programme.
Pyongyang is under international sanctions for its nuclear weapons and ballistic missile programmes.
Stanford University's Dr Siegfried Hecker believes Kim has enough resources to build 45 nukes and could reach much of Japan, but that his arsenal needs more testing.
The despot and former US President Donald Trump engaged in a charm offensive, which even saw them reportedly exchange 'love letters'.
But their multiple nuclear summits appeared to be ultimately fruitless and likely did little to build any lasting relationship between the two countries.
The two leaders failed to agree on what Kim would give up in exchange for sanctions relief seeing the summit ending abruptly by Trump in November 2019.
Scott A Snyder, senior fellow for Korea studies and director of the programme on US-Korea policy at the Council on Foreign Relations (CFR) , claims the danger remains.
He said Barack Obama warned Trump before leaving office that North Korea was the "most vexing" international security threat he faced.
"Two nuclear tests, myriad long-range missile tests, and three Trump-Kim summits later, the magnitude and likelihood of North Korea posing a catastrophic threat to US national interests is greater than it was four years ago," he added.
