An Iranian nuclear scientist long suspected by the West of masterminding a secret atomic weapons programme was assassinated near Tehran on Friday, Iranian state media reported.
Mohsen Fakhrizadeh died of injuries in hospital after armed assassins fired on his car, Iranian media reported.
Fakhrizadeh has long been described by Western, Israeli and Iranian exile foes of Iran's clerical rulers as a leader of a covert atomic bomb programme halted in 2003. Iran has long denied seeking to weaponise nuclear energy.
"Unfortunately, the medical team did not succeed in reviving (Fakhrizadeh), and a few minutes ago, this manager and scientist achieved the high status of martyrdom after years of effort and struggle," Iran's armed forces said in a statement carried by state media.
The semi-official news agency Tasnim said earlier that "terrorists blew up another car" before firing on a vehicle carrying Fakhrizadeh and his bodyguards in an ambush outside the capital.
Fakhrizadeh is thought to have headed what the UN nuclear watchdog and US intelligence services believe was a coordinated nuclear weapons programme in Iran, shelved in 2003.
He has the rare distinction of being the only Iranian scientist named in the International Atomic Energy Agency's 2015 "final assessment" of open questions about Iran's nuclear programme and whether it was aimed at developing a nuclear bomb.
Zarif says Israel likely to be involved
Iran's foreign minister said Iran's arch-enemy Israel was likely to have been involved in the killing of prominent Iranian nuclear scientist Mohsen Fakhrizadeh on Friday, although he offered no evidence.
"This cowardice - with serious indications of Israeli role -shows desperate warmongering of perpetrators," Mohammad Javad Zarif tweeted. "Iran calls on int'l community - and especially EU - to end their shameful double standards & condemn this act of state terror."
Israeli Prime Minister Benjamin Netanyahu's office was not commenting on reports of the attack, an official from Netanyahu's office said. The Pentagon also declined to comment.