North Korea has started expanding a uranium enrichment facility at the Yongbyon nuclear complex, according to NK Pro analysis of satellite imagery, following leader Kim Jong Un’s orders to “exponentially” increase the country’s nuclear weapons stockpile.

Planet Labs imagery shows construction started in mid-September on a new annex to the original uranium enrichment (UE) building at Yongbyon.

While the purpose of the construction is unclear, the shape and area of the annex is similar to one added to the same building five years ago, as well as an annex built in 2024 at a second UE facility in Kangson, near the capital.

State media for the first time published photos of Kim Jong Un inspecting thousands of centrifuges at what appeared to be the Kangson facility in Sept. 2024 and Yongbyon a few months later. 

North Korea also built a brand new UE facility — the country’s third known site — at the Yongbyon complex last year, which Kim appeared to inspect in June. 

• Read more: New uranium plant brings North Korea closer to mass-producing nukes

A high-resolution Maxar satellite image taken on Monday showed a roughly 1,300-square-meter (14,000 square feet) L-shaped annex being built on the southeast corner of the old Yongbyon UE building. 

Blue-colored roofing was already installed over most of the annex, suggesting authorities have attached a high level of urgency to the project. 

The International Atomic Energy Agency (IAEA) recently reported that it believed new centrifuge cascades built inside the similar annex built at Kangson started to be operational in January, about 22 months after construction began. 

IAEA chief Rafael Grossi said in April that North Korea’s efforts to expand enrichment capabilities have resulted in a “very serious increase in the area of nuclear weapons production, which is estimated at a few dozen warheads.” 

The Stockholm International Peace Research Institute (SIPRI) estimated North Korea “had probably assembled around 60 warheads and possessed enough fissile material to potentially produce at least 90 warheads” as of January.

During his apparent visit to Yongbyon in June, Kim Jong Un ordered “ambitious future plans designed to strengthen our state’s nuclear forces exponentially.”

The leader called for “accelerating” nuclear weapons development at a party plenum that same month and “bolstering up the nuclear force both in quality and quantity” at a military meeting in July. 

Edited by David Choi