Recent satellite images show North Korea is expanding a uranium enrichment plant at its main Yongbyon nuclear complex, a sign it's intent on boosting the production of bomb materials, experts say.
The assessment comes after North Korea recently performed its first missile tests in six months amid long-dormant nuclear disarmament diplomacy with the United States.
"The expansion of the enrichment plant probably indicates that North Korea plans to increase its production of weapons-grade uranium at the Yongbyon site by as much as 25 per cent," Jeffrey Lewis and two other experts at Middlebury Institute of International Studies at Monterey said in a report.
The report said satellite images taken by Maxar show construction in an area adjoining the uranium enrichment plant at Yongbyon.
A satellite image taken on September 1 shows North Korea cleared trees and prepared the ground for construction, with a construction excavator also visible.
The report said a second image taken on September 14 showed a wall erected to enclose the area, work on a foundation and panels removed from the side of the enrichment building to provide access to the newly enclosed area.
"The new area is approximately 1000 square metres, enough space to house 1000 additional centrifuges," the report said.
"The addition of 1000 new centrifuges would increase the plant's capacity to produce highly enriched uranium by 25 per cent."
Nuclear weapons can be built using either highly enriched uranium or plutonium, and North Korea has facilities to produce both at Yongbyon.
Last month, earlier satellite photos on Yongbyon showed signs North Korea was resuming the operation of other facilities to produce weapons-grade plutonium.
North Korea calls the Yongbyon complex "the heart" of its nuclear program.
US and South Korean experts speculate North Korea is covertly running multiple other uranium-enrichment plants.
In 2018, a top South Korean official told parliament North Korea was estimated to have already manufactured up to 60 nuclear weapons as well.
In the past week, North Korea launched both ballistic and cruise missiles toward the sea in tests seen as an effort to diversity its missile forces and strengthen its attack capability on South Korea and Japan, where a total of 80,000 American troops are based.
Experts say both types of missiles could be armed with nuclear warheads.
Australian Associated Press