Hamas and Iran's paramilitary Revolutionary Guard said early Wednesday that Hamas leader Ismail Haniyeh has been killed in the Iranian capital, Tehran.

"The residence of Ismail Haniyeh, head of the political office of Hamas Islamic Resistance, was hit in Tehran," said a statement by the Islamic Revolutionary Guard Corps' (IRGC) Sepah news website.

"The cause is under investigation and will be announced soon," the IRGC said. One of his bodyguards was also killed, it added.

Condemnation amid fear of wider conflict

Iran's Supreme Leader Ayatollah Ali Khamenei vowed that "harsh punishment" awaited Israel for the attack, and that it was Iran's duty to avenge his death.

In a separate statement, the militant group Hamas said Haniyeh was killed after he attended the inauguration of the new Iranian President 

"Brother, leader, mujahid Ismail Haniyeh, the head of the movement, died in a Zionist strike on his headquarters in Tehran after he participated in the inauguration of the new [Iranian] president," Hamas said in its own statement.

Russia, Turkey, Qatar and the Palestinian Authority, of which Hamas is not a part, all condemned the strike.

The killing of Haniyeh comes amid mounting fears that the conflict in Gaza, which has already spilled over into Lebanon, Syria and Yemen, could erupt into a regional war.

Who was Ismail Haniyeh?

Haniyeh joined Hamas in 1987, during the group's founding amidst the backdrop of a major uprising against Israel.

He became Palestinian prime minister in 2006, though rival factions disputed the legitimacy of his position for years. He was elected leader of Hamas' political bureau in 2017.

He had been living in exile in Qatar and Turkey since 2016. He was said to maintain good relationships with various Palestinian factions since then. In recent months, he had met with political leaders in both Iran and Turkey on diplomatic missions.

Hamas led the terror attacks against Israel on October 7 in which 1,200 people, mostly civilians, were killed and some 250 hostages were taken to Gaza.

The Palestinian militant group is designated as a terrorist organization by Israel, the US and Germany, among others. In response, Israel launched a military operation in Gaza that has killed more than 39,000 in the enclave, with more killed in strikes in Lebanon and Yemen.

fb,es/jsi (AP, AFP, Reuters, dpa)