The Islamic Republic and its allies have blamed Israel for Haniyeh’s killing on July 31 during a visit to the Iranian capital for the swearing-in of President Masoud Pezeshkian. Israel has not commented.
Iran has vowed to avenge the death, which came hours after an Israeli strike in Beirut killed a senior commander of Hezbollah, the powerful Iran-backed militant group in Lebanon.
Western diplomats have scrambled to avert a major conflagration in the Middle East, where tensions were already high due to the Israel-Hamas war in Gaza.
In a statement, the United States and its European allies urged Iran to de-escalate.
The White House warned that a significant set of attacks by Iran and its allies was possible as soon as this week, saying Israel shared the same assessment.
The United States has deployed an aircraft carrier strike group and a guided missile submarine to the region in support of Israel.