The attack was praised by US President Donald Trump's Republicans but elsewhere there were sharp warnings it could inflame regional tensions.
Following are some of the reactions from around the world.
'Severe revenge'
"Martyrdom was the reward for his ceaseless efforts in all these years," Iran's supreme leader Ayatollah Ali Khamenei said on Twitter.
"With him gone, God willing, his work and his path will not be stopped, but severe revenge awaits the criminals who bloodied their foul hands with his blood and other martyrs' in last night's incident."
Khamenei said he was killed by "the most cruel of those on earth".
"The lack of our devoted and dear general is bitter, but continuing the fight and achieving final victory will embitter the murderers and criminals even more."
| Twitter Post |
'Spark a devastating war'
Iraq's caretaker prime minister Adel Abdel Mahdi said the US strike, which also killed an Iraqi commander, would "spark a devastating war".
"The assassination of an Iraqi military commander in an official post is an aggression against the country of Iraq, its state, its government and its people," he said.
It was a "flagrant violation of the conditions authorising the presence of US troops" on Iraqi soil.
'Meting out punishment'
"Meting out the appropriate punishment to these criminal assassins... will be the responsibility and task of all resistance fighters worldwide," the leader of Lebanon's Hezbollah Shiite militant group, Hassan Nasrallah, said in a statement.
"We will carry a flag on all battlefields and all fronts and we will step up the victories of the axis of resistance with the blessing of his pure blood."
'Aggravate situation'
"This action can seriously aggravate the situation in the region," Russian President Vladimir Putin said, according to a Kremlin readout of a phone conversation with French counterpart Emmanuel Macron.
Konstantin Kosachev, head of the foreign affairs committee of parliament's upper house, said on Facebook the killing was a mistake that would strike back at Washington.
"Retaliatory strikes will certainly follow."
| This action can seriously aggravate the situation in the region - Russian President Vladimir Putin |
'Appeal for restraint'
"China has always opposed the use of force in international relations," foreign ministry spokesman Geng Shuang said.
"We urge the relevant sides, especially the United States, to remain calm and exercise restraint to avoid further escalating tensions."
He said Iraq's sovereignty, independence and territorial integrity must be respected.
'Price of killing Americans'
"In a display of resolve and strength, we struck the leader of those attacking our sovereign US territories," top House of Representatives Republican Kevin McCarthy said.
"Wow - the price of killing and injuring Americans has just gone up drastically," tweeted Senator Lindsey Graham, a close confidant of Trump.
But among Democrats, US House Speaker Nancy Pelosi said the killing risks provoking a "dangerous escalation of violence".
"President Trump just tossed a stick of dynamite into a tinderbox," his 202 presidential rival Joe Biden said.
"Iran will surely respond. We could be on the brink of a major conflict across the Middle East."
| Twitter Post |
'Threaten peace and stability'
"Pakistan has viewed with deep concern the recent developments in the Middle East, which seriously threaten peace and stability in the region," the foreign ministry said.
"Respect for sovereignty and territorial integrity are the fundamental principles of the UN Charter, which should be adhered to. It is also important to avoid unilateral actions and use of force."
The foreign ministry in neighbouring India said: "We have noted that a senior Iranian leader has been killed by the US. The increase in tension has alarmed the world."
'Against foreign intervention'
"It is manifest that the operation carried out by the US will increase insecurity and instability in the region... Turkey has always been against any foreign intervention in the region, assassinations and sectarian conflicts," the foreign ministry said.
'World more dangerous'
"We have woken up to a more dangerous world," France's Europe Minister Amelie de Montchalin told French radio.
"In such operations, when we can see an escalation is under way, what we want above all is stability and de-escalation.
"Our role is not to take sides, but to talk with everyone."
British Foreign Secretary Dominic Raab said London had "always recognised the aggressive threat" posed by Soleimani and his Quds Force. "Following his death, we urge all parties to de-escalate. Further conflict is none of our interests."
The Netherlands also urged de-escalation.
"It is of great importance that tranquility is preserved in the region. Nobody benefits from further escalation," tweeted Dutch Foreign Minister Stef Blok whose country has taken part in the anti-IS coalition since 2014.
'Methods of criminal gangs'
Syria is "certain that this cowardly US aggression... will only strengthen determination to follow in the path of the resistance's martyred leaders," a foreign ministry official said, according to state news agency SANA.
The official said the killings were "a serious escalation" and accused the US of resorting to "the methods of criminal gangs".