Addressing the volatile situation after the killing of Qasem Soleimani, those representing various countries and factions warned that the world has become a more dangerous place after the incident, and urged restraint on all sides.
The USA's targeted killing of the Iranian top general could ignite conflict in the region, according to an Al Jazeera report quoting several world leaders.
The killing marks a major escalation in the standoff between the Washington and Tehran. The US-Iran relations have careened from one crisis to another since US President Donald Trump withdrew from the 2015 nuclear deal, and imposed crippling sanctions.
Here is how the world players and regional factions have responded to the incident.
UN Secretary General Antonio Guterres is deeply concerned by the recent rise in tensions in the Middle East, his spokesperson said in a statement.
"The secretary general has consistently advocated for de-escalation in the Gulf," Farhan Haq said, adding, "This is a moment in which leaders must exercise maximum restraint. The world cannot afford another war in the Gulf."
French President Emmanuel Macron and his foreign minister were reaching out to "all the actors in the region," said France's Deputy Minister for Foreign Affairs, Amelie de Montchalin.
"We are waking up in a more dangerous world. Military escalation is always dangerous. When such actions, such operations, take place, we see that escalation is underway," Amelie de Montchalin said on RTL radio.
Montchalin indicated that urgent reconciliation efforts are being launched behind the scenes.
Russia's foreign ministry condemned the killing of Soleimani and said it will increase tensions throughout the Middle East. An unnamed diplomat in the ministry told Russia's state-run news agency TASS that they consider the killing "an adventurist step."
The head of the foreign affairs committee in Russia's upper parliament house called the US airstrike "a mistake" that could "boomerang on its organizers."
Foreign Affairs Committee Chairman Konstantin Kosachev in a Facebook post on Friday, stated that the move destroyed the last hope for resolving the issues around the Iran nuclear deal.
"Iran may accelerate making a nuclear weapon now, even if it didn't plan on doing it before," Kosachev said.
Russian foreign ministry spokesperson Maria Zakharova recently said in a TV interview that there were no legal grounds for the strike.
China, meanwhile, said it is "highly concerned" and called for all sides, especially the USA, to exercise "calm and restraint."
China is a close Iranian ally and has been among the most active countries in defying USA's attempts to isolate Iran and cripple its economy. Last month, its navy joined with those of Iran and Russia in first-ever joint drills in the Indian Ocean.
China is also a staunch opponent of the US presence in Iraq.
Foreign Ministry spokesperson Geng Shuang said on Friday that China is calling for peace and stability in the Middle East, as well as respect for Iraq's independence and territorial integrity.
"China has always opposed the use of force in international relations," said the spokesman, warning against the further escalation of tensions.
Chancellor Angela Merkel's spokeswoman Ulrike Demmer urged restraint and de-escalation.
"We are at a dangerous point of escalation. It is now important through prudence and restraint to contribute to the de-escalation," said an Al Jazeera report quoting Demmer.
Foreign Minister Heiko Maas said that the aim now is to prevent further escalation across the Middle East.
"We are making use of our diplomatic channels to Iran and to other states in the region," he said, adding, "Since this morning, we have been in close contact with our British and French partners and with other European countries on how we can best work to calm the situation."
UK Foreign Minister Dominic Raab urged all parties to de-escalate after the airstrike.
"We have always recognized the aggressive threat posed by the Iranian Quds force led by Qasem Soleimani. Following his death, we urge all parties to de-escalate. Further conflict is in none of our interests," he said in an emailed statement to Reuters.
US Secretary of State Mike Pompeo said that he spoke to Raab and China's top diplomat Yang Jiechi about the US decision to eliminate Soleimani, and that Washington is committed to "de-escalation."
The Turkish foreign ministry said that the killing of Soleimani will increase insecurity and instability in the region.
In a written statement, the ministry said it was deeply concerned by the rising tensions between the USA and Iran, and that turning Iraq into an area of conflict will harm peace and stability in the region.
"Turkey has always been against foreign interventions, assassinations and sectarian conflicts in the region," Al Jazeera reported quoting the ministry.
Israeli Prime Minister Benjamin Netanyahu said on Friday that the United States had the right to defend itself by killing Soleimani.
"Just as Israel has the right of self-defense, the United States has exactly the same right," Netanyahu said in a statement issued by his office.
"Qassim Soleimani is responsible for the death of American citizens and many other innocent people. He was planning more such attacks."
Israel Army Radio said that the military has gone on heightened alert amid fears that Iran could launch a strike through its regional allies, after the USA killed General Soleimani.
Netanyahu spoke on the airport tarmac in Greece after cutting short a trip abroad to fly back to Israel.
"President Trump deserves all the credit for acting swiftly, forcefully and decisively. Israel stands with the United States in its just struggle for peace, security and self-defense."
Prime Minister Adel Abdul-Mahdi condemned the strike as an "aggression against Iraq" and a "blatant attack on the nation's dignity."
He also called for an emergency session of parliament to take "necessary and appropriate measures to protect Iraq's dignity, security and sovereignty" on Saturday, when funerals were scheduled to be held in Baghdad for Al-Muhandis, the militia commander, and the other slain Iraqis.
Iraq has been gripped by massive anti-government protests since October, partly against Iran's influence over the country. But at least one protester, who asked not to be named for security concerns, said they "do not celebrate" the killing of Soleimani, reported CBS.
"America and Iran should solve their problems outside Iraq," he said, adding, "We do not want them to solve it inside Iraq, because this will not serve our cause."
The Syrian government, which has received key support from Iran throughout the civil war, also condemned the strike.
The government said the incident could lead to a "dangerous escalation" in the region.
Hassan Nasrallah, the head of the Iran-backed Lebanese militant group Hezbollah, released a statement mourning those killed in the US air strike, saying their blood was not wasted.
He called for the death of Soleimani to be avenged.
"Meting out the appropriate punishment to these criminal assassins ... will be the responsibility and task of all resistance fighters worldwide," Nasrallah said in a statement, adding, "We who stayed by his side will follow in his footsteps, and strive day and night to accomplish his goals."
In the Gaza Strip, the Hamas militant group offered its "sincerest condolences" to Iran, saying Soleimani had "played a major and critical role in supporting the Palestinian resistance at all levels."
For Iran, the killing represents the loss of a cultural icon who represented national pride and resilience while facing US sanctions. While careful to avoid involving himself in politics, Soleimani's profile rose sharply as the US and Israel blamed him for Iranian proxy attacks abroad.
Iran's Supreme Leader Ayatollah Ali Khamenei warned a "harsh retaliation is waiting" for the USA after the airstrike, calling Soleimani the "international face of resistance."
Khamenei declared three days of public mourning for the general's death.
He also appointed Soleimani's deputy, Brig Gen Esmail Ghaani, to replace him as the head of the country's Quds Forces, Iranian media reported.
The force's programme "will remain unchanged from the time of his predecessor," Khamenei said in a statement published by state media.
Iran summoned the Swiss chargé d'affaires, who represents US interests in Tehran, to protest the killing.
"The chargé d'affaires was informed of Iran's position and in turn delivered the message of the United States," the ministry said in an emailed response to a Reuters query, without elaborating further.
Trump sent out a tweet of an American flag shortly after the attack. He said on Friday that Soleimani "should have been taken out many years ago."
"Soleimani has killed or badly wounded thousands of Americans over an extended period of time, and was plotting to kill many more...but got caught! He was directly and indirectly responsible for the death of millions of people, including the recent large number of PROTESTERS killed in Iran itself," he wrote in a pair of Tweets.
"While Iran will never be able to properly admit it, Soleimani was both hated and feared within the country. They are not nearly as saddened as the leaders will let the outside world believe," added the US president.
The United States urged its citizens to leave Iraq "immediately."
The State Department said the embassy in Baghdad, which was attacked by Iran-backed militia and other protesters earlier this week, is closed and all consular services have been suspended.
Around 5,200 US troops are based in Iraq, where they mainly train Iraqi forces and help combat ISIS.