Iran's armed forces chief of staff Major General Mohammad Bagheri warned of "severe revenge" for those behind the assassination Friday of a top nuclear scientist outside Tehran.

"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.

Iran's Zarif says 'serious indications of Israeli role' in scientist killing

Iran's Foreign Minister Mohammad Javad Zarif has claimed there were "serious indications of (an) Israeli role" in the assassination of a nuclear scientist on Friday.

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

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