The prominent Iranian nuclear scientist Mohsen Fachrisadeh is said to have been killed in an attack near Tehran.
After an armed attack, he was treated in hospital and died of his injuries there, reports in the Iranian state media said on Friday.
According to the semi-official Fars news agency, Fachrisadeh's car was shot at.
Eyewitnesses also reported an explosion.
While Fachrisadeh has been referred to as a “martyr” in the state media, he is suspected by Western states and Israel as well as by opponents of the Iranian leadership living in exile of having been the architect of a covert nuclear weapons program that was discontinued in 2003.
The Islamic Republic has long denied the pursuit of nuclear weapons.
The Fars news agency reported that the attack took place in Absard, a small town outside Tehran.
Several injured, including Fachrisadeh's bodyguard, were taken to hospital.
Photos and videos allegedly from the crime scene showed a car with bullet holes in the windshield and blood on the road.
"Murdering nuclear scientists is the most violent course to keep us from reaching modern science," wrote Hossein Salami, commander of the influential Iranian Revolutionary Guard, on Twitter.
Hossein Deghan, adviser to Iran's highest leader Ayatollah Ali Khamenei, directly accused Israel and threatened those responsible.
"In the last days of the political life of their gambling ally, the Zionists are trying to intensify and increase the pressure on Iran in order to wage an all-out war," he wrote on Twitter, apparently referring to US President Donald Trump.
"We will descend like a bolt of lightning on the murderers of this oppressed martyr and make them regret their actions."
In Absard, where the attack is believed to have taken place, there are numerous weekend houses for the Iranian elite.
From there you have a view of the Damawand, the largest mountain in the country.
The streets were emptier than usual on Friday due to a corona lockdown, which also resulted in few eyewitnesses.
Open questions about the Iranian nuclear program
The International Atomic Energy Agency (IAEA) had mentioned Fachrisadeh's name in a final report in connection with open questions about the Iranian nuclear program and in particular whether it was aimed at the development of a nuclear bomb.
The IAEA report from 2015 states that Fachrisadeh monitored the activities "in support of a possible military dimension of the (Iranian) nuclear program" as part of the so-called AMAD plan.
Israel has also referred to the AMAD plan as Iran's secret nuclear weapons program.
According to Israeli Prime Minister Benjamin Netanyahu, Fachrisadeh is said to have continued to work on "special projects" for the Ministry of Defense in Tehran.
Netanyahu's office did not comment on the scientist's death.