As News of Iran's Supreme Leader's Death Spread, Reactions Ranged From Public Celebrations to Vows of Vengeance. The Fallout Has Laid Bare Deep Regional Divides Over Iran's Role and Growing Unease About Israel's Expanding Military Reach

People in Iran took to the streets as they mourned over the death of the country's supreme leader Ayatollah Ali Khamenei, who was killed in US-Israeli strikes.

Thousands of mourners gathered Sunday in the center of Iran's capital, while some celebrated elsewhere after the death of Iran's supreme leader,...