The predawn killing of a top Hamas leader in Tehran, Iran, on Wednesday left the entire Middle East on edge, bringing vows of revenge from Iran¡¯s leaders and threatening to derail fragile negotiations for a ceasefire in the Gaza Strip.

The Hamas leader, Ismail Haniyeh, 62, a top negotiator in the ceasefire talks who had led the militant group¡¯s political office in Qatar, was killed after he and other leaders of Iranian-backed militant groups had attended the inauguration of Iran¡¯s new president.

Israeli leaders would not confirm or deny whether their country was behind the brazen breach of Iran¡¯s defenses. But Iranian leaders and Hamas officials immediately blamed Israel and vowed to avenge the death of Haniyeh, heightening fears of a broader regional war.