A U.S. institute tracking North Korea’s nuclear weapons program says recent satellite photos show Pyongyang is doubling the size of its uranium enrichment plant, jibing with the country’s announced plans to expand technology that can be used both to create energy and the core of nuclear weapons, according to The Associated Press.

The imagery comes from two sources, satellite companies Digital Globe and Astrium Geoinformation Services, and was seen by the AP ahead of publication by the Institute for Science and International Security on Wednesday. In an accompanying note, ISIS said the photos of the Nyongbyon nuclear complex show construction under way to “effectively double” the size of the enrichment hall.

That, said ISIS, would allow North Korea to also double the number of centrifuges now enriching uranium. Revealing the existence of a uranium enrichment program three years ago, Pyongyang said the plant contained 2,000 centrifuges — machines that are linked up in series and spin uranium gas into material that can be used either to power reactors or arm nuclear weapons, depending on the degree of enrichment.

That means the 4,000 centrifuges that the space is apparently being expanded for could potentially make twice that amount, giving them the capacity to build up to four bombs a year — should the country decide to use them for that purpose.

The most recent satellite photo was taken July 28. ISIS says that measured against earlier images, it shows construction at the Nyongbyon site, including “the expansion of the gas centrifuge building” to twice its previous size.

The Washington-based think tank said the images indicate that work on the structure seems to have begun sometime in March. It cited a North Korean government announcement that came shortly afterward revealing plans for “readjusting and restarting all the nuclear facilities in Nyongbyon, including (the) uranium enrichment plant.”