The world braced on Sunday for Iran's response after the U.S. attacked key Iranian nuclear sites, joining Israel in the biggest Western military action against the Islamic Republic since its 1979 revolution.

Iran vowed to defend itself a day after the U.S. dropped 30,000-pound bunker-buster bombs onto the mountain above Iran's Fordow nuclear site while American leaders urged Tehran to stand down and pockets of anti-war protesters emerged in U.S. cities.