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"Once again, the wicked hands of the global arrogance, with the usurper Zionist regime as the mercenary, were stained with the blood of a son of this nation," Rouhani said in a statement on his official website, referring to the

Iran generally uses the term "global arrogance" to refer to the United States.

Rouhani’s comments came after  armed forces chief of staff Major General Mohammad Bagheri warned of "severe revenge" for those behind the assassination.

"Terrorist groups and the leaders and the perpetrators of this cowardly attempt should know that severe revenge awaits them," he said in a tweet reported by state news agency IRNA.

Bagheri called the death of Mohsen Fakhrizadeh "a bitter and heavy blow" and added "we assure (Iranians) that we will not rest until we have chased and punished" those involved.

The tweet comes shortly after Iran's Foreign Minister Mohammad Javad Zarif said on Twitter that there were "serious indications of (an) Israeli role" in the assassination of Fakhrizadeh. 

"Terrorists murdered an eminent Iranian scientist today. This cowardice - with serious indications of Israeli role - shows desperate warmongering of perpetrators," Zarif said.

He also called on the international community to "end their shameful double standards and condemn this act of state terror."

The Iranian semi-official Tasnim news agency reported that Mohsen Fakhrizadeh - widely viewed as the architect of  contentious nuclear  - was shot dead in the small Iranian city of Absard east of Tehran.

Another semi-official news agency, Fars, said witnesses heard the sound of an explosion and then machine gun fire. The attack targeted a car that Fakhrizadeh was in.

The area around Absard is filled with vacation villas for the Iranian elite with a view of Mount Damavand, the highest peak in the country. Roads on Friday, during Iran’s weekend, were emptier than normal due to a lockdown over the coronavirus pandemic, offering his attackers a chance to strike with fewer people around.

The wounded, including Fakhrizadeh's bodyguards, were later taken to a local hospital, according to Fars.

State television on its website later published a photograph of security forces blocking off the road. Photos and video shared online showed a Nissan sedan with bullet holes through the windshield and blood pooled on the road.

Ex-CIA chief condemns 'criminal' assassination 

Meanwhile, the former head of the US  labelled the  of a top  nuclear scientist Friday a "criminal" act that risks inflaming conflict in the region.

John Brennan said he did not know who was to blame for the murder of Mohsen Fakhrizadeh, as Tehran pointed its finger at Israel.

"This was a criminal act & highly reckless. It risks lethal retaliation & a new round of regional conflict," Brennan said in a series of tweets.

"I do not know whether a foreign government authorized or carried out the murder of Fakhrizadeh," he said.

"Such an act of state-sponsored terrorism would be a flagrant violation of international law & encourage more governments to carry out lethal attacks against foreign officials."

Brennan noted that Fakhrizadeh was not a designated terrorist nor a member of Al Qaeda or the Islamic State group, designated terror groups which would be legal targets.

A strong critic of President Donald Trump, Brennan urged Tehran to "resist the urge" to retaliate and "wait for the return of responsible American leadership on the global stage," a reference to November 3 election winner Joe Biden, who will replace Trump on January 20.

Brennan was director of the CIA from 2013 to 2017, under the administration of president Barack Obama and then-vice president Biden.

Agencies contributed to this report.

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