Iran held funeral processions on Thursday for Hamas political chief Ismail Haniyeh after he was killed in a strike in Tehran blamed on Israel.

The Islamic republic’s supreme leader Ayatollah Ali Khamenei led the prayers for Haniyeh ahead of his burial in Doha, having earlier threatened a “harsh punishment” for his killing.

In the capital’s city centre, mourning crowds carrying posters of Haniyeh and Palestinian flags gathered at Tehran University on Thursday morning, according to an AFP correspondent.

Haniyeh’s death was announced the day before by Iran’s Revolutionary Guards, who said he and his bodyguard were killed in a strike on their accommodation in the Iranian capital at 2:00 am (2230 GMT) on Wednesday.

It came just hours after Israel targeted and killed top Hezbollah commander Fuad Shukr in a retaliatory strike on the Lebanese capital Beirut, sending fears of a wider regional war soaring.

Israel has declined to comment on the Tehran strike.

Khamenei, who has the final say in Iran’s political affairs, said after Haniyeh’s death that it was “our duty to seek revenge for his blood as he was martyred in the territory of the Islamic Republic of Iran”.

The Hamas leader was in Tehran for the inauguration ceremony of newly elected President Masoud Pezeshkian on Tuesday.

The Iranian president said Wednesday that “the Zionists (Israel) will soon see the consequences of their cowardly and terrorist act”.

Hamas political bureau member Musa Abu Marzuk also vowed retaliation, saying: “The assassination of leader Ismail Haniyeh is a cowardly act and will not go unanswered.”

The international community, however, called for de-escalation and a focus on securing a ceasefire in Gaza.

UN Secretary-General Antonio Guterres said the strikes in Tehran and Beirut represented a “dangerous escalation”.

All efforts, he said, should be “leading to a ceasefire” in Gaza and the release of hostages taken during Hamas’s October 7 attack on southern Israel.

US Secretary of State Antony Blinken also said Wednesday that a ceasefire in Gaza was still the “imperative”, with White House National Security Council spokesman John Kirby later adding that the twin killings “don’t help” regional tensions.

From the early hours of Wednesday, crowds took to the streets in cities across Iran and the Middle East to condemn Haniyeh’s killing, with hundreds gathering in Tehran’s Palestine Square to chant “Death to Israel, Death to America”.

The Islamic republic has not yet published any information on the exact location of the strike.

While Iran has blamed the attack on its arch-foe, Israel has declined to comment on Haniyeh’s death. It did, however, claim the killing of Shukr, whom it blamed for a deadly weekend rocket strike on the Israeli-annexed Golan Heights.

The killings come with regional tensions already inflamed by the war in Gaza, a conflict that has drawn in Iran-backed militant groups in Syria, Lebanon, Iraq and Yemen.

One of those groups, Yemen’s Houthi rebels, “declared three days of mourning” for Haniyeh, with political leader Mahdi al-Mashat expressing “condolences to the Palestinian people and Hamas” over his killing, according to the group’s Saba news agency.

Saudi Foreign Minister Prince Faisal bin Farhan, meanwhile, spoke by phone after the attack with his acting Iranian counterpart Ali Bagheri to discuss “the latest developments in the region”.

The UN Security Council also convened an emergency meeting Wednesday at Iran’s request to discuss the strike, with Tehran’s envoy Amir Saeid Iravani urging members to take “immediate action to ensure accountability for these violations of international law”.

Hamas has for months been indirectly negotiating a truce and hostage-prisoner exchange deal with Israel, with Egypt, Qatar and the United States facilitating the talks.

Analysts told AFP that Haniyeh was a moderating influence within the Islamist group, and that while he would be replaced, the dynamics within Hamas could change.