The government of Israel–which has not acknowledged its stockpile or development of nuclear weapons–has started a construction project at a highly-sensitive nuclear weapons site, the Associated Press reports.

Satellite photos of the Shimon Peres Negev Nuclear Research Center near the city of Dimona show excavation larger than a football field near an existing underground facility that extracts plutonium from spent nuclear power plant rods.  The plutonium is then processed into weapons-grade material.

The International Panel on Fissile Materials at Princeton University spotted the construction last week on photos taken by a commercial satellite; the AP then commissioned a different commercial satellite company to provide higher-resolution images.  The site was original constructed by the Israelis, with French assistance, in the 1950s.  It’s become the center for Israeli nuclear research and development.

Analysts believe that the nuclear reactor at Dimona may be facing decommissioning in the near future, forcing Israel to build another nuclear plant at the site to continue to enrich plutonium.

“I believe that the Israeli government is concerned to preserve and maintain the nation’s current nuclear capabilities,” said Avner Cohen, a professor of nonproliferation studies at the Middlebury Institute of International Studies at Monterey.  “If indeed the Dimona reactor is getting closer to decommissioned, as I believe it is, one would expect Israel to make sure that certain functions of the reactor, which are still indispensable, will be fully replaced.”

Israel has been a vocal critic of Iran developing nuclear capabilities while failing to acknowledge its own nuclear weapons programs.