Hamas Political Bureau Chairman Ismail Haniyeh was assassinated in the Iranian capital of Tehran, Iran's Islamic Revolution Guards Corps 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.

Ebrahim Rezaei, a spokesperson for 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.

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

Palestinian Authority President Mahmoud Abbas also slammed the killing as "a cowardly act and a serious escalation," his office said in a statement. "He urged our people and their forces to unite, remain patient, and stand firm against the Israeli occupation," the statement added.

Qatar and Egypt, which have acted as mediators in ceasefire negotiations between Israel and Hamas, said on Wednesday that the killing of Haniyeh could jeopardize efforts to secure a truce in Gaza.

"The approach of political assassinations and intentional escalation against civilians in Gaza at every stage of the negotiation prompts the question: How can negotiations take place in which one party kills its negotiator at the same time?" Qatari Prime Minister Sheikh Mohammed bin Abdulrahman Al Thani wrote on X.

Egypt's Foreign Ministry said in a statement that a "dangerous Israeli escalation policy" over the past two days had undermined efforts to broker an end to the fighting in Gaza.

"The coincidence of this regional escalation with the lack of progress in the ceasefire negotiations in Gaza increases the complexity of the situation and indicates the absence of Israeli political will to calm it down," the statement said.

"It undercuts the strenuous efforts made by Egypt and its partners to stop the war in the Gaza Strip and put an end to the human suffering of the Palestinian people," it added.

Malaysia's Ministry of Foreign Affairs said in a statement that Malaysia strongly condemns the assassination of Haniyeh and extends its deepest condolences and sympathies to the family members, as well as to the leadership and people of Palestine.

"Malaysia urges for an immediate and thorough investigation into this assassination, and those responsible to be brought to justice," according to the statement. 

Malaysia also urged all parties to exercise restraint while the facts surrounding the assassination were being established. "The incident underscores the urgent need for de-escalation and reinforces the necessity for all parties to engage in constructive dialogue and pursue peaceful resolutions."

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.

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 Afghan caretaker government also expressed condolences over the death of Haniyeh, according to a spokesperson for the administration.

"We extend our heartfelt condolences to Haniyeh's grieving family, the leadership of Hamas," Zabihullah Mujahid said in a statement posted on social media.

Chinese Foreign Ministry spokesperson Lin Jian said on Wednesday that China is highly concerned about the death of Haniyeh and firmly opposes and condemns the assassination.

"We are greatly concerned about the incident, firmly oppose and condemn the assassination, and are deeply worried that this incident may lead to further instability in the region," Lin said.

U.S. Secretary of State Antony Blinken said that reaching a ceasefire in Gaza "is the enduring imperative" after the killing of Haniyeh. Germany stressed international calls for restraint to avoid "a regional conflagration," with a Foreign Ministry spokesman saying: "The logic of tit-for-tat reprisals is the wrong path."

(With input from Xinhua, Reuters, AFP)