Israel attacked Iran’s capital early Friday, with explosions booming across Tehran.

The attack comes as tensions have reached new heights over Tehran’s rapidly advancing nuclear program. The Board of Governors at the International Atomic Energy Agency for the first time in 20 years on Thursday censured Iran over it not working with its inspectors. Iran immediately announced it would establish a third enrichment site in the country and swap out some centrifuges for more-advanced ones.

Israel for years has warned it will not allow Iran to build a nuclear weapon, something Tehran insists it doesn’t want — though official there have repeatedly warned it could. The U.S. has been preparing for something to happen, already pulling some diplomats from Iraq’s capital and offering voluntary evacuations for the families of U.S. troops in the wider Middle East.