President Hassan Rouhani has said Iran will retaliate for the assassination of suspected top nuclear scientist 'at the proper time'.
Mohsen Fakhrizadeh was ambushed and killed near Tehran and in what 'officials' are calling a terrorist attack.
Rouhani has accused Israel of the killing which happened on November 27.
In a speech which was televised on Saturday November 28, the president said: "Our people are wiser than to fall in the trap of the Zionist regime (Israel) ... Iran will surely respond to the martyrdom of our scientist at the proper time."
This comes after an Iranian military commander said Iran would strike back against killers who carried out the attack.
“We will strike as thunder at the killers of this oppressed martyr and will make them regret their action,” Hossein Dehghan, military adviser to Iranian Supreme Leader Ayatollah Ali Khamenei, wrote in a tweet.
The United Nations Secretary-General Antonio Guterres urged restraint.
We have noted the reports that an Iranian nuclear scientist has been assassinated near Tehran today.
"We urge restraint and the need to avoid any actions that could lead to an escalation of tensions in the region," Guterres' spokesman Farhan Haq said.
Reports claim Western officials have long believed Fakhrizadeh was the head of Iran's secretive nuclear programme.
The Ministry of Defence confirmed the death of the physics professor and leading figure in Iran's Revolutionary Guard.
Iran's Foreign Minister Mohammad Javad Zarif claimed there were indications of an Israeli role in the scientist's death
He demanded that Western nations, and particularly the European Union, condemn the 'act of state terror' immediately.
He wrote in a tweet: "Terrorists murdered an eminent Iranian scientist today.
"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."
The Pentagon has declined to comment on the incident, Reuters reports.
It is believed Fakhrizadeh was a key figure in developing the means to assemble a nuclear warhead behind the facade of a declared civilian uranium enrichment programme.
Iran denies ever having sought to develop a nuclear weapon.
Believed to be a senior officer in the elite Revolutionary Guard, Fakhrizadeh was the only Iranian the report identified.
