TEHERAN/GAZA - Hamas Politburo Chief Ismail Haniyeh has been killed in the Iranian capital of Teheran, Iran's Islamic Revolution Guards Corps (IRGC) confirmed on Wednesday.

Haniyeh and his bodyguard were killed early Wednesday when their residence was hit in Tehran, according to a statement published on the IRGC's official news outlet Sepah News.

The statement said the attack was under investigation and the results would be announced later.

In a report published on Wednesday, Iran's semi-official Fars news agency said Haniyeh was assassinated around 2:00 am local time (2230 GMT Tuesday) after his residence in Teheran was hit by a "projectile."

The Islamic Hamas movement confirmed the death of its leader, saying Haniyeh was assassinated by an Israeli attack in Iran.

In a press statement, Hamas said that it "mourns to the Palestinian people, the Arab and Islamic nation, and the free people of the world" after the death of Haniyeh, who was in Teheran to attend the swearing-in ceremony of Iranian President Masoud Pezeshkian on Tuesday.

Haniyeh was also expected to discuss with the Iranian president the political and field developments related to the current Palestinian-Israeli conflict in the Gaza Strip, a source close to Hamas told Xinhua.

Ebrahim Rezaei, a spokesman of the Iranian parliament's National Security and Foreign Policy Committee, told reporters that the committee would convene a meeting later in the day to investigate and discuss the incident.

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Referring to Haniyeh's assassination as a "cowardly" move, he said those behind it would undoubtedly receive a "necessary response."

Russian Deputy Foreign Minister Mikhail Bogdanov said on Wednesday that Haniyeh's death is an "absolutely unacceptable political assassination."

Quoted by Russia's RIA Novosti, Bogdanov warned that the incident could lead to further escalation in the region and have a significantly negative impact on the negotiations in Doha.

Türkiye also condemned the assassination, saying that the attack "aims to spread the war in Gaza to the region."

"It has been revealed once again that the (Israeli Prime Minister Benjamin) Netanyahu government has no intention of achieving peace," the Turkish foreign ministry said in a statement on Wednesday.

"Unless the international community takes action to stop Israel, our region will face much greater conflicts," it said.

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Lebanese Prime Minister Najib Mikati condemned the assassination of Haniyeh during a cabinet meeting, warning of "a serious danger of expanding the circle of danger in the region."

Hezbollah on Wednesday also offered its condolences for Haniyeh's "martyrdom," calling him "one of the great resistance leaders in our present era who stood with all courage in the face of the American hegemony project and the Zionist occupation."

The Israeli army has no comment yet.

Since Oct 7 last year, Israel has been launching a large-scale strike on Hamas.

According to Gaza health authorities, the Israeli offensive has led to the killing of over 38,000 Palestinians in the enclave, while the UN estimated that nearly 2 million people there have been displaced.

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"This assassination by the Israeli occupation of Brother Haniyeh is a grave escalation that aims to break the will of Hamas," senior Hamas official Sami Abu Zuhri told Reuters.

He said Hamas would continue the path it was following, adding: "We are confident of victory."

Haniyeh, normally based in Qatar, has been the face of the Palestinian group's international diplomacy since the war started on Oct 7 in Gaza, where three of his sons were killed in an Israeli airstrike.

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Appointed to the Hamas top job in 2017, Haniyeh has moved between Türkiye and Qatar's capital Doha, escaping the travel curbs of the blockaded Gaza Strip and enabling him to act as a negotiator in ceasefire talks.

With Reuters inputs