Iran has started up new cascades of advanced centrifuges and plans to install others in the coming weeks after facing criticism over its nuclear program, the United Nations’ atomic watchdog said Friday. The U.S. called the moves “nuclear escalations.”

Spinning up new centrifuges further advances Iran’s nuclear program, which already enriches uranium at near-weapons-grade levels and boasts a stockpile enough for several nuclear bombs if it chose to pursue them.

However, the…