Guterres earlier urged restraint in response to the killing, a United Nations spokesperson said.
"Assassinating nuclear scientists is the most violent confrontation to prevent us from reaching modern science", Mr Salami tweeted.
The U.S. Departments of State and Treasury started sanctioning Fakhrizadeh in 2008, blocking him from interacting with the U.S. financial system.
Former CIA director John Brennan warned the assassination risked sparking a wider conflagration in the Middle East. "Iranian leaders would be wise to wait for the return of responsible American leadership on the global stage & to resist the urge to respond against perceived culprits".
"This Friday afternoon, armed terrorist elements attacked a auto carrying Mohsen Fakhrizadeh, head of the Ministry of Defense's Research and Innovation Organization". The scientist was rushed to a local hospital where doctors were unable to revive him.
As Fakhrizadeh's sedan stopped on the wide, tree-lined avenue, five or six gunmen emerged from a nearby vehicle and opened fire on his auto, the semi-official Tasnim news agency said.
Mohsen Fakhrizadeh, 59, was "seriously wounded" when assailants targeted his auto before being engaged in a gunfight with his bodyguards, the defence ministry said.
Others wounded included Fakhrizadeh's bodyguards.
"Remember that name, Fakhrizadeh", Mr Netanyahu said at the time, displaying a rare photo of him on a slide.
Hossein Salami, chief commander of the paramilitary Guard, appeared to acknowledge the attack on Fakhrizadeh. "This is how Dr. Mohsen Fakhrizadeh, head of Project Amad, put it".
"We will strike as thunder at the killers of this oppressed martyr and will make them regret their action". In the United States, the White House, Pentagon, State Department and Central Intelligence Agency all declined to comment, as did Mr Biden's transition team. Here's more on the man whose killing is being blamed on Israel.
A view of the reactor building at the Bushehr nuclear power plant in southern Iran.
Fakhrizadeh led Iran's so-called Amad (Hope) programme.
In probing Iran's past nuclear activities, IAEA had long sought to interview Fakhrizadeh.
While the assassination is a setback for Iran's nuclear program, the program doesn't rely on just one scientist and will certainly continue after Fakhrizadeh's death.
Tensions with Iran under the Trump administration came to a head after the United States withdrew unilaterally from the Joint Comprehensive Plan of Action (JCPOA) in May 2018 and began to reimpose sanctions previously lifted under the nuclear deal. Iran has since breached the pact by expanding R&D on advanced centrifuges for enriching uranium.
Iran has endured months of mysterious sabotage targeting missile and nuclear and missile installations as well as an assassination campaign targeting scientists involved in atomic research between 2010 and 2012.
But the killing also also underscores serious security lapses exploited by probable anti-regime operatives who were able to penetrate the country and bypass heavy layers of surveillance imposed by authorities.
