Hamas political leader Ismail Haniyeh was killed on Wednesday in an Israeli strike in Iran, the group said, in an act that has stunned the international community.
Israel has not commented on the death but many countries have warned that it will have a major impact on efforts to bring a ceasefire in the Gaza war. Here are the key reactions:
-- Palestinian president calls killing 'cowardly'
Palestinian Authority president Mahmud Abbas is a rival of Haniyeh but slammed the killing as "cowardly".
"President Mahmud Abbas of the State of Palestine strongly condemned the assassination of Hamas leader Ismail Haniyeh, deeming it a cowardly act and a serious escalation," Abbas's office said in a statement.
"He urged our people and their forces to unite, remain patient, and stand firm against the Israeli occupation."
-- Iran vows to defend 'territorial integrity'
Haniyeh had been in Tehran to attend the inauguration of President Masoud Pezeshkian, who commented on the X social platform: "The Islamic Republic of Iran will defend its territorial integrity, honour, pride and dignity, and make the terrorist invaders regret their cowardly action."
-- Qatar and Turkey warn of 'chaos'
Haniyeh was based in Qatar, which has been a mediator in the Gaza conflict, but also spent time in Turkey after going into exile in 2017. Qatar's foreign ministry called the killing a "heinous crime" and "shameful assassination".
The ministry said the strike in Tehran was a "dangerous escalation" and "a flagrant violation of international and humanitarian law".
"This assassination and the reckless Israeli behaviour of continuously targeting civilians in Gaza will lead to the region slipping into chaos and undermine the chances of peace".
Turkey echoed the condemnation. "We condemn the assassination of the leader of Hamas's political office, Ismail Haniyeh, in a shameful assassination in Tehran," the foreign ministry said, adding that "this attack also aims to spread the Gaza war to a regional dimension".
"Once again the (Benjamin) Netanyahu government has shown that it has no intention of achieving peace," the ministry said. "If the international community does not take measures to stop Israel, our region will face much larger conflicts."
Meanwhile, Qatar's Prime Minister Sheikh Mohammed bin Abdulrahman Al-Thani on Wednesday cast doubt on the success of future mediation between Israel and Hamas following the killing of the Palestinian group's political chief Ismail Haniyeh in Tehran.
"Political assassinations & continued targeting of civilians in Gaza while talks continue leads us to ask, how can mediation succeed when one party assassinates the negotiator on other side? Peace needs serious partners," Sheikh Mohammed, who has led Qatar's mediation efforts, wrote on X.
Russia and China condemn
Haniyeh went to Moscow in September 2022 for talks on the Israel-Palestinian conflict while Hamas and rival Palestinian faction Fatah held talks in Beijing last week.
"It is a completely unacceptable political assassination, and this will lead to a further escalation of tensions," Russia's Deputy Foreign Minister Mikhail Bogdanov told the state-run RIA Novosti news agency.
Konstantin Kosachev, the vice-president of Russia's upper house Federation Council, predicted a "sudden escalation of mutual hatred" in the Middle East.
China's foreign ministry spokesman Lin Jian said: "We are highly concerned about the incident and firmly oppose and condemn the assassination."
-- Hamas allies rally
Hamas allies in the region rallied around the Palestinian fighters.
"The martyrdom of leader Haniyeh... will increase the determination and stubbornness of the mujahideen resistance fighters on all resistance fronts... and will make their resolve stronger in confronting the Zionist enemy," Lebanese militants Hezbollah, who are in a growing standoff with Israel, said in a statement.
The group described Haniyeh as "one of the great resistance leaders of our time who stood bravely against the American hegemony project and the Zionist occupation."
"Targeting him is a heinous terrorist crime and a flagrant violation of laws and ideal values," said Mohammed Ali al-Huthi, a member of the political bureau of Yemen's Huthi rebels who have staged rocket attacks on Israel. Afghanistan's Taliban rulers called Haniyeh's death "a great loss".
Syria says killing could 'set region ablaze'
Syria's foreign ministry condemned the killing of Hamas leader Ismail Haniyeh on Wednesday, blaming Israel and warning that the latest escalation could "set the entire region ablaze".
"Syria condemns this blatant Zionist aggression," the ministry said, describing Haniyeh's killing as a "despicable act" and adding it "considers that the continued disregard of international laws by the Israeli entity... may set the entire region ablaze".
Iraq says killing could threaten region's stability
Iraq on Wednesday condemned the killing in Tehran of Hamas political leader Ismail Haniyeh, warning that it threatens the region's stability.
Iraq's foreign ministry in a statement described the killing as a "flagrant violation of international law and a threat to security and stability in the region".
The Al-Nujaba movement, part of a pro-Iran alliance in Iraq, said "the Zionists and Americans have opened the doors of hell" following the killing if Haniyeh, the targeting of a Hezbollah commander in Beirut, and a US strike on pro-Iran combatants in Iraq.
These "assassinations... will not deter us, but strengthen our determination", it added.
In recent months, the Islamic Resistance in Iraq, a loose alliance of pro-Iran groups including Al-Nujaba, has claimed to have targeted Israel with drone and rocket strikes against targets.
The Israeli army, without naming an attacker, has confirmed several aerial attacks from the east since April, but has said they were all intercepted before entering its airspace.
The alliance had also claimed attacks on US troops in Syria and Iraq for more than three months, as regional tensions soared over the Israel-Hamas war in Gaza, before suspending them in late January.
Afghan Taliban terms killing 'a great loss'
Afghanistan's Taliban government said Wednesday the killing of Hamas political leader Ismail Haniyeh in neighbouring Iran was "a great loss", hailing him as "an intelligent and resourceful Palestinian leader".
"He was successful and left the lessons of resistance, sacrifice, patience, tolerance, struggle and practical sacrifice to his followers," Taliban government spokesman Zabihullah Mujahid said in a statement.
Australia sees 'profound' risks for escalation
Australia's defence minister warned of "profound" risks for further escalation in the Middle East Wednesday, after Israel was blamed for an audacious assassination of Hamas' political leader on Iranian soil.
Richard Marles said the killing of Ismail Haniyeh in Tehran, while apparent retribution for Hamas' bloody October 7 attacks on Israel, created a moment of deep peril for a region already roiled by crisis. "This individual was central to the activities which occurred on October 7, activities which we have consistently condemned," Marles said.
"That said, we have consistently been advocating for a ceasefire in the Middle East to see an end to the catastrophe which is playing out in the Middle East" he said.
Australia -- like many Western nations -- has backed Israel's right to defend itself. But it has also been cautiously critical of the Jewish state's prosecution of the war in Gaza, and in particular the deaths of untold Palestinian civilians.
Marles reflected a new sense of peril after Wednesday's killing of Haniyeh -- which could prompt a military response from Hamas, Iran or its proxies across the Middle East and could complicate fitful negotiations to free hostages still held by Hamas.
"I think all of us look at what's occurring in the Middle East and want to see an end to the catastrophe that is playing out," he said.
"We definitely want to ensure that we do not see an escalation in what's playing out in the Middle East because the consequences of that would be profound."
Haniyeh was attending the inauguration of Iran's new president when he was killed by an Israeli air strike, Hamas said.
He is by far the most high-profile Palestinian leader to be killed since the October 7 attacks.
Hamas vowed the "cowardly" killing of their veteran leader "will not go unanswered".
Israel did not immediately claim responsibility for the attack, but such a high-stakes operation deep inside Iran would signify a major coup for Israeli intelligence and the country's embattled prime minister Benjamin Netanyahu.
Erdogan condemns 'perfidious assassination' of Hamas chief
Turkish President Recep Tayyip Erdogan on Wednesday condemned the "perfidious assassination" in Tehran of his close ally and "brother" Ismail Haniyeh, the political leader of Islamist Palestinian movement Hamas.
"May God have mercy on my brother Ismail Haniyeh, fallen in martyrdom after this odious attack," Erdogan wrote on the X social media platform, denouncing "Zionist barbarity".
"This shameful act aims to sabotage the Palestinian cause, the glorious Gazan resistance and our Palestinian brothers' just fight, and to intimidate Palestinians," Erdogan added.
Turkey's foreign ministry had earlier denounced the attack as "a shameful assassination".
Haniyeh, who spent much time in Turkey before the October 7 attacks launched by Hamas on Israel, last paid a visit to Erdogan in Istanbul in April.
While Hamas is viewed by the United States, the European Union and Israel as a terrorist organisation, Erdogan described it as "a liberation movement".
Since 2011 and an agreement that saw more than 1,000 Palestinian prisoners released in exchange for the captured Israeli soldier Gilad Shalit, Turkey has provided a refuge for Hamas officials.
Yemen rebels call killing 'terrorist crime'
The killing of Hamas's political leader in an air strike in Tehran is a "heinous terrorist crime", Yemen's Iran-backed Huthi rebels said on Wednesday.
"Targeting him is a heinous terrorist crime and a flagrant violation of laws and ideal values," Mohammed Ali al-Huthi, a member of the group's political bureau, posted on X.