What is known so far about the killing of Hamas leader and fears of a major war in the Middle East

The killing of Hamas political leader Ismail Haniyeh in an Israeli army strike in Tehran risks the outbreak of a major war in the Middle East as world diplomacy calls for calm and peace.

As Iran warns of fierce retaliation with a pattern of drone and missile barrages on Israel on April 14, Israeli Defense Minister Yoav Galant said Israel is against war but is preparing for all eventualities.

As the chief diplomat of an ally of Israel, US Secretary of State Antony Blinken said that Washington had no prior knowledge of the assassination that had been organized for the head of Hamas. Blinken said the event showed how important the ceasefire is in the Gaza Strip.

Through the X network, Turkish President Recep Tayyip Erdo?an called the murder of Ismail H Haniyeh, with whom he had fraternal political relations, a Zionist barbarism.

For the Russian Foreign Ministry, this is a political assassination that could spiral tensions in the Middle East out of control.

Representatives of Qatar and Egypt, who have been pushing and mediating relentlessly to achieve peace between Israel and Hamas, reacted strongly, saying that the killing of Haniyeh destroys the ceasefire efforts.

This is what is known so far:

Hamas political leader Ismail Haniyeh was killed while visiting Iran's capital Tehran, just hours after Hezbollah's top military commander Fu'ad Shukr was killed in an Israeli strike in Beirut, plunging the region into a new unrest.

While Israel claimed responsibility for the attack on Shukr, it has not done so for the attack on Iran, with the military saying it "does not respond to foreign media reports".

Who was Haniyeh? He has been part of Hamas for decades, in recent years running the militant group's political operations from exile and emerging as one of its most visible leaders during the war with Israel in Gaza. He was a key interlocutor with international mediators in the hostage and cease-fire talks between Israel and Hamas.

And about the timing: Haniyeh was killed on the first day of the new Iranian president Masoud Pezeshkian's term. He was in Iran for Pezeshkian's inauguration. Iran has been a major supporter of Hamas.

What regional leaders said: Haniyeh's killing has shocked regional leaders, with Qatar calling it a "dangerous escalation" and Turkey's president calling it a "despicable act".

US reaction: Secretary of State Antony Blinken, during a visit to Singapore, said the United States was "not aware of or involved in" Haniyeh's murder. In an interview from Singapore, the top US diplomat said he would not speculate on the impact of the assassination.

Iranian Supreme Leader's Statement: Iran's Supreme Leader Ayatollah Ali Khamenei said it was the nation's duty to avenge Haniyeh's death since he was killed on their soil. "You killed our beloved guest in our home and now you have opened the way for your harsh punishment," he said, referring to Israel.

Why does killing him matter? His killing is a significant blow to the Palestinian militant group - and comes at a difficult time for the Middle East, with escalating confrontations between Israel and Hezbollah threatening to escalate into a regional war. It also calls into question the future of Israel-Hamas negotiations.