Iranian physicist Mohsen Fakhrizadeh, the alleged head of Iran's nuclear program, was shot and killed in a purported assassination near Tehran, said the country's Ministry of Defense.
The Iranian Ministry of Defense confirmed Fakhrizadeh was "severely wounded in the course of clashes between his security team and terrorists and was transferred to hospital," according to Iranian state-run media. He later died from his wounds.
No groups have claimed responsibility for the incident.
He wrote on Twitter "terrorists murdered an eminent Iranian scientist today. This cowardice—with serious indications of Israeli role—shows desperate warmongering of perpetrators."
Zarif then accused the European Union and the "international community" of engaging in a "shameful double standard."
Western intelligence agencies had considered Fakhrizadeh the chief architect of Iran's controversial nuclear program who was potentially overseeing the development of a nuclear weapon on behalf of the regime. Iranian officials have long insisted that the country's nuclear program is for strictly peaceful purposes.
The Iranian Revolutionary Guards Corps commander said on Twitter that Iran will get revenge for the killing.
"We will strike as thunder at the killers of this oppressed martyr and will make them regret their action," commander Hossein Dehghan, who is also a military adviser to Iranian Supreme Leader Ayatollah Ali Khamenei, wrote after the incident.
According to Tasnim News, Fakhrizadeh was gunned down in Absard city near Damavand, which is around 40 miles east of Tehran. It furthermore reported that several others were killed in the incident.
Some local reports suggested that suicide bombers may have been involved in the incident, although it's not clear.
Fakhrizadeh was a senior Iranian Revolutionary Guards Corps (IRGC) officer and was also a professor of physics at the Imam Hussein University in Tehran. Some analysts suggested that his death is as momentous as the death of Iran's Quds Force commander Qassem Soleimani earlier this year, which prompted Tehran to launch a volley of missiles at U.S. assets in Iraq.
Reports in 2015 described the scientist as the Iranian version of J. Robert Oppenheimer, the American physicist who directed the Manhattan Project that produced the first atomic weapons for the United States during World War II.
Israel has not commented on the incident.