China is pursuing plans to develop floating nuclear reactors that could power military facilities it has built in contested areas of the South China Sea, according to the top U.S. military commander in the Pacific and State Department officials, a prospect they warn would undermine regional security and stability.

After more than a decade of research and development and Chinese regulators’ safety concerns, China appears to be moving forward with its plans — at a time when the international community has not yet crafted standards governing floating reactors’ safe use, U.S. officials said.