Iran's top nuclear scientist Mohsen Fakhrizadeh has been assassinated near the capital Tehran, the country's defence ministry has confirmed.
Mohsen Fakhrizadeh, who was considered one of the masterminds of Iran's controversial nuclear program, died after his car was apparently ambushed in a district east of Tehran.
Fakhrizadeh died in hospital after an attack in Absard, in Damavand county.Photos from the scene showed the shattered windshield of a car, and blood on the road.
Iran's Foreign Minister Mohammad Javad Zarif, has condemned the killing "as an act of state terror".
"Terrorists murdered an eminent Iranian scientist today," Zarif said in a tweet.
"This cowardice -- with serious indications of Israeli role -- shows desperate warmongering of perpetrators Iran calls on int'l community -- and especially EU -- to end their shameful double standards & condemn this act of state terror."
Ali Akbar Velayati, international affairs adviser to Iran's Supreme Leader Ayatollah Ali Khamenei, said in a statement: "The Iranian nation will avenge the blood of this great martyr from the terrorist elements and their supporters."
Major General Mohammad Bagheri, the chief of staff of the Iranian Armed Forces, warned of "severe revenge" against "the killers" of Fakhrizadeh, state-news agency IRNA reported.
Fakhrizadeh was head of the research centre of new technology in the elite Revolutionary Guards, and was a leading figure in Iran's nuclear programme for many years.
He has long been spoken about by Western security sources as extremely powerful and instrumental in Iran's nuclear programme.
According to secret documents obtained by Israel in 2018, he led a programme to create nuclear weapons. At the time, Israeli Prime Minister Benjamin Netanyahu said he identified Fakhrizedeh as the head scientist in the programme, and urged people to "remember that name".
Recently, Fakhrizadeh has been identified as the most prominent face of a nuclear programme that has been the main flashpoint in an international dispute. He is mentioned in multiple reports by the US State Department and the International Atomic Energy Agency as holding deep insight into Iran's nuclear capabilities.
It's unclear what role he held in Iran's efforts -- always officially denied -- to develop a nuclear weapon. It is also not clear how much he would know of the most secret elements of anything Iran may be doing, given his profile. But he was a symbol of Iran's past ambitions, and was protected heavily.
Meanwhile, tensions between the US and Iran have escalated, peaking in January with America's assassination of Gen Qasem Soleimani, commander of the Iranian Revolutionary Guards' Quds force.
There are just over 50 days left in the Trump administration, before President-elect Joe Biden is inaugurated and diplomatic contacts between Tehran and Washington are likely to pick up again.
There are many in Israel and the US who see the current "maximum pressure" policy of sanctions and hostility as the only route to stop Iran from expanding its influence and getting the bomb eventually.