Mohsen Fakhrizadeh was injured after gunmen shot at his car and he later died in hospital, Iranian state media reported.
Hossein Dehghan, adviser to Iran’s supreme leader and candidate for election in the country next year, warned the perpetrators and appeared to add his voice to claims that Israel carried out the attack.
“In the final days of their gaming ally’s political life, the Zionists seek to step up and increase pressure on Iran to wage a full-fledged war,” Dehghan wrote, referring to the US President Donald Trump.
“We will descend like lightning on the assassins of this oppressed martyr and we will make them regret their actions!” ”
Mr. Trump has sharply criticized the Iranian nuclear project throughout his presidency and has been seen as an ally of Israel and Benjamin Netanyahu.
Israel has long alleged that Fakhrizadeh led a military nuclear program in the early 2000s, but the country declined to comment after Friday’s news.
The country’s mission to the United Nations described Fakhrizadeh’s work, saying he was overseeing efforts to produce a coronavirus vaccine and “the development of the first indigenous COVID-19 test kit.”
The attack occurred in Absard, a small town just east of the capital Tehran, according to the semi-official Fars news agency, which is believed to be close to the Revolutionary Guards.
State television said a truck containing explosives hidden under a pile of wood exploded near a car carrying Mr. Fakhrizadeh.
As the car stopped, at least five gunmen got out and shot at the vehicle, the semi-official Tasnim news agency said.
Photos and videos circulating online showed a Nissan sedan with bullet holes through the windshield and blood stains on the road.
People injured in the attack, including the nuclear scientist’s bodyguards, were then taken to a local hospital, Tasnim said.
Although no group immediately claimed responsibility for the attack, Iranian media noted the interest Israeli Prime Minister Benjamin Netanyahu had previously shown in the nuclear scientist.
Mr. Netanyahu called him out at a press conference in 2018, saying, “Remember that name,” referring to Mr. Fakhrizadeh.