Iran held a funeral ceremony with calls for revenge after the killing in Tehran of Hamas political chief Ismail Haniyeh in a strike blamed on Israel.
Thousands of mourners paid respects to Mr Haniyeh as the Israeli military confirmed that an air strike in Gazalast month killed the Hamas military chief, Mohammed Deif.
Iran's supreme leader Ayatollah Ali Khamenei led prayers for Mr Haniyeh ahead of his burial in Qatar, having earlier threatened a "harsh punishment" for his killing.
In Tehran's city centre, crowds, including women shrouded in black, carried posters of Mr Haniyeh and Palestinian flags in a procession and ceremony that began at Tehran University.
Iran's Revolutionary Guards announced yesterday that Mr Haniyeh and a bodyguard were killed in a pre-dawn strike on their accommodation in Tehran.
It came just hours after Israel killed a top Hezbollah commander, Fuad Shukr, in a retaliatory strike in the south of Lebanon's capital Beirut, raising fears of a wider regional conflict as the Israel-Hamas war in Gaza continues.
Shukr is to be buried today.
Senior Iranian officials including President Masoud Pezeshkian and the Islamic Revolutionary Guard Corps chief, General Hossein Salami, attended the ceremony for Haniyeh, state TV showed.
Qatar-based Haniyeh had been visiting Tehran for Mr Pezeshkian's inauguration ceremony on Tuesday.
Khalil al-Hayya, Hamas's foreign relations chief, vowed during the funeral ceremony that Mr Haniyeh's message will live on and "we will pursue Israel until it is uprooted from the land of Palestine".
Mr Pezeshkian later told Hayya that Iran "will continue to support with firmer determination the Axis of Resistance", Iran-aligned regional groups that include Hamas, the official IRNA news agency said.
The caskets carrying Mr Haniyeh and his bodyguard, with a black-and-white pattern resembling a Palestinian keffiyeh scarf, were borne on a flower-decorated truck through city streets jammed with mourners cooled by water spray on a hot day.
Iran's parliamentary speaker Mohammad Bagher Ghalibaf said, "It is our duty to respond at the right time and in the right place," as crowds chanted "Death to Israel, Death to America!"
The New York Times, citing Iranian officials, reported that Ayatollah Khamenei has ordered Iran to strike Israel directly.
The international community called for calm and a focus on securing a ceasefire in Gaza - which Mr Haniyeh had accused Israel of obstructing.
United Nations Secretary-General Antonio Guterres said the strikes in Tehran and Beirut represented a "dangerous escalation".
The UN Security Council convened an emergency meeting yesterday at Iran's request to discuss the incident.
In a phone call, the foreign ministers of Jordan and Egypt blamed Israel for rising tensions and "stressed the need to work on de-escalation to prevent the region from slipping into a comprehensive regional conflict", Jordan's official Petra news agency reported.
United States Secretary of State Antony Blinken has reiterated appeals for an end to fighting. He said achieving peace "starts with a ceasefire" and called on "all parties" to "stop escalatory actions".
But the prime minister of key ceasefire broker Qatar said Mr Haniyeh's killing had thrown the whole Gaza war mediation process into doubt.
"How can mediation succeed when one party assassinates the negotiator on the other side?" Sheikh Mohammed bin Abdulrahman Al-Thani said on social media site X.
Iran has blamed the attack on Israel, however Israel has declined to comment on Mr Haniyeh's death.
But it did claim the killing of Hezbollah commander Shukr, blaming him for a weekend rocket strike that killed 12 children and teenagers in the Israeli-annexed Golan Heights.
The killings are the latest of several incidents that have inflamed regional tensions during the Gaza war which has drawn in Iran-backed militant groups in Syria, Lebanon, Iraq and Yemen.
Yemen's Houthi rebels declared three days of mourning for Mr Haniyeh. Earlier this month they claimed a drone strike on Tel Aviv, their first fatal attack in Israel, which retaliated against Yemen's rebel-controlled Hodeida port.
In April, after a strike killed Revolutionary Guards at its consulate in Damascus, Iran made its first ever direct attack on Israeli soil, firing a barrage of drones and missiles.
Explosions later hit central Iran, in what US media said was Israeli retaliation.
Israeli Prime Minister Benjamin Netanyahu has vowed to destroy Hamas in retaliation for its 7 October attack on Israel that ignited the war in Gaza.
That attack resulted in the deaths of 1,197 people, mostly civilians, according to an AFP tally based on official Israeli figures.
Militants also seized 251 hostages, 111 of whom are still held captive in Gaza, including 39 the military says are dead.
Concern over the fate of those still held has grown among Israelis, who have demonstrated by the tens of thousands demanding a deal to free them.
Mr Haniyeh's killing "was a mistake as it threatens the possibility of having a hostage deal," said Anat Noy, a resident of Haifa.
Israel's retaliatory campaign against Hamas has killed at least 39,480 people in Gaza, according to the Hamas-run territory's health ministry, which does not give details of civilian and militant deaths.
An Israeli military statement said Mohammed Deif, head of Hamas's armed wing, was killed by Israeli warplanes on July 13 in a strike in Gaza's Khan Younis area.
Gazan health authorities said at the time that the strike killed more than 90 people but Hamas denied Deif was among them.
