Iran is set to hold funeral processions for Ismail Haniyeh, the Hamas political chief who was killed in Tehran in what the Islamist militant group said was an Israeli strike.
Ayatollah Ali Khamenei, the supreme leader of Iran, will lead the prayers for Haniyeh, state media said. Haniyeh will later be buried in Qatar.
Khamenei has vowed a "harsh punishment" for Haniyeh's killing and said it was Iran's "duty" to seek revenge as he was assassinated on Iranian soil.
Israel has not claimed responsibility for the attack, although Prime Minister Benjamin Netanyahu said Israel had delivered "crushing blows" to Iran's proxies over the last few days.
Haniyeh's death came just hours after Israel killed top Hezbollah commander Fuad Shukr in a strike on the Lebanese capital, Beirut, following an attack on the Israeli-occupied Golan Heights. Israel accused Hezbollah of carrying out the strike that killed a dozen children.
The latest developments have prompted concerns internationally of a wider regional conflict.
Who was Ismail Haniyeh?
Ismail Haniyeh was born in a Gaza refugee camp in 1962 and attended a United Nations school. He joined Hamas in 1987 at the beginning of a major uprising against Israel known as the first Intifada.
Haniyeh was appointed prime minister of the Palestinian Authority by President Mahmoud Abbas after Hamas won a majority of seats in the 2006 legislative elections.
However, Abbas tried to dismiss him when Hamas unleashed a wave of violence to oust his Fatah party from the Gaza Strip. Haniyeh refused to step down and Hamas continued to rule the Gaza Strip, while Fatah remained responsible for the occupied West Bank.
Haniyeh moved to Qatar to live in exile in 2016. In 2017, he was elected head of Hamas' political bureau, succeeding Khaled Mashaal.
Israel had vowed to kill him following the October 7 Hamas attack on Israeli civilians.
The Hamas militant group is designated as a terrorist organization by Israel, the United States and Germany, among others.