Iran’s top nuclear scientist was killed Friday in an alleged assassination that the country’s foreign minister linked to Israel. Mohsen Fakhrizadeh, considered one of the masterminds of Iran’s controversial nuclear program, died after his car was apparently ambushed in a district east of Tehran. Photos from the scene showed the shattered windshield of a car, and blood on the road. Iranian state media said the killing appeared to be an assassination. Iran’s Defense Minister Brigadier General Amir Hatami was quoted by Iran’s semi-official news agency ISNA as saying Fakhrizadeh was targeted by gunfire and a Nissan vehicle explosion, before a firefight ensued. Iranian Foreign Minister Zarif called the death “cowardice – with serious indications of Israeli role.” Israeli Prime Minister Benjamin Netanyahu’s office declined to comment to CNN. Fakhrizadeh was head of the research center of new technology in the elite Revolutionary Guards, and was a leading figure in Iran’s nuclear program for many years. “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.” US President Donald Trump retweeted prominent Israeli journalist Yossi Melman, who wrote: “Fakhrizadeh-Mahabadi assassinated in Damavand, east of Tehran according to reports in Iran. He was head of Iran’s secret military program and wanted for many years by Mossad. His death is a major psychological and professional blow for Iran.” The Trump administration said it was closely monitoring the apparent assassination. The death “would be a big deal,” a US official told CNN. Several top-level Iranian officials have condemned the attack and threatened to retaliate. The head of Iran’s Revolutionary Guards Corps, Hossein Salami, issued a statement calling the killing a “terrorist operation”, according to ISNA. “The blinded enemies of Iran, particularly the planners and coordinators of this cowardly act of terrorism must understand that such savagery will not cause a single wrinkle in our collective will to conquer bright scientific horizons, and be aware that the difficult revenge awaiting them is already an integral part of our work!,” he said, according to the news agency. 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.” The Chief of Staff of the Iranian Armed Forces, Major General Mohammad Bagheri, warned of “severe revenge” against “the killers” of Fakhrizadeh, state-news agency IRNA reported. “The assassination of this capable and worthy manager, although it was a bitter and heavy blow to the country’s defense complex, but the enemies know that the path started by the martyr Fakhrizadeh will never be stopped,” Bagheri said, according to IRNA. Lebanon’s Hezbollah, the Iran-backed Lebanese militant group, also condemned the killing. Hezbollah’s second-in-command, Naim Qassem, said that agents of the US and Israel were behind the assassination. “We condemn this sinful attack, and we see that the response to this crime is in the hands of those concerned in Iran. We are not shaken by assassinations,” Qassem said during an interview with Hezbollah-owned al-Manar TV. Trita Parsi, the co-founder and executive vice president of the Quincy Institute for Responsible Statecraft, said it was not clear who was behind the apparent assassination, but that “there are not that many candidates.” “At the end of the day the only countries that actually have the intent, the motivation and the capacity – and the capacity is really important – really reduces the number of candidates to no more than Israel and potentially the United States,” he told CNN’s Becky Anderson. In April 2018, Netanyahu mentioned Fakhrizadeh by name when he unveiled a nuclear archive he said Mossad agents had taken from Tehran. He called him the head of a secret nuclear project called Project Amad. “Remember that name, Fakhrizadeh,” Netanyahu told reporters. Iran began to withdraw from its commitments to the 2015 landmark nuclear deal in 2019, a year after US President Donald Trump pulled out of the agreement and unleashed crippling sanctions on the country. In the last month, the International Atomic Energy Agency documented several new breaches of the agreement. Earlier this week, Iran said it had begun injecting Uranium Hexafluoride gas into centrifuges at its Natanz facility. Why was Fakhrizadeh targeted? Fakhrizadeh is the most prominent face of nuclear program 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. That did did not stop him being targeted and killed in broad daylight in the outskirts of Iran’s capital. The message is clear: Iran’s enemies can kill its nuclear celebrities anywhere. Is the timing significant? 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. Fakhrizadeh’s killing makes that kind of diplomacy harder, and gives voice to hawks in Iran that peacemaking is futile. It also gives voice to Iran’s enemies, who can argue that taking on Iran head first is possible and can be palpably a deterrent. While the apparent assassination is embarrassing to Iran, it wants diplomacy with Biden rather than outright conflict. Iran has yet to respond, beyond condemnation, to the killing of Iranian military commander Qassem Soleimani earlier this year. Again, Tehran may prefer to blame its enemies loudly and then move on, rather than seek open conflict. This story has been updated to standardize the spelling of Fakhrizadeh’s name.