Bangladesh, Dec. 5 -- Nigers military government has launched an extraordinary attack on the French state-owned nuclear company Orano, accusing it of environmental destruction, public endangerment, and violations of national sovereignty. The accusations-described by officials as “mass crimes”-represent the most serious escalation to date in a rapidly deteriorating relationship between Paris and its former colony, which for decades supplied uranium crucial to Frances nuclear-powered energy grid.

The confrontation took on a dramatic new dimension after Nigerien officials announced the discovery of about 400 abandoned barrels of radioactive core materials near the former Madaouela uranium site in the countrys northern desert reg...