The researchers compared satellite photos taken during the past four months with images captured within the past week, finding the missile site covering a grid of hundreds of square kilometers in China's Gansu province, said researcher Jeffrey Lewis, a Chinese nuclear weapons expert who examined the images with colleague Decker Eveleth, the first person to spot the silos.
The pair's findings were first reported in the Washington Post. Lewis told CNN on Friday that most of the silo construction, which has yet to be completed, has likely occurred in the past six months.