North Korea has started to expand a suspected nuclear facility near Pyongyang, according to NK Pro analysis of satellite imagery, after leader Kim Jong Un called for increasing nuclear weapon production last year.

Planet Labs and Airbus images of the main building at the Kangson site alleged to house uranium enrichment operations show workers have been building a new annex along the length of the rear (west) side of the building since last month.

A new rear wall around 395 feet long (120 meters) was built about 40 feet (12 meters) away from the rear of the building, while