TEHRAN: A top Iranian official Monday said nuclear scientist Mohsen Fakhrizadeh was killed in a new type of "complex operation", blaming arch-foe Israel and an exiled opposition group.

The "operation was very complex, using electronic equipment and no one was present at the scene," the secretary of Iran's Supreme National Security Council, Rear-Admiral Ali Shamkhani said.

The People's Mujahedeen of Iran (MEK) were "certainly" involved, along with "the Zionist regime and the Mossad", Shamkhani said, referring to the Israeli government and its external security agency.

"The enemy used a completely new, professional and specialised method and reached its goal," he added, without elaborating on the weaponry involved. Shamkhani's comments came in video interviews broadcast by state television and the Fars news agency.

Without citing sources, Fars itself claimed that the attack had been carried out with the help of "a remote controlled automatic machine gun" mounted on a pick up truck.

Iran's President Hassan Rouhani had Saturday accused Israel of acting as a "mercenary" for the United States by carrying out the assassination.

The scientist Mohsen Fakhrizadeh died on Friday from his wounds in a hospital, according to Iran's defence ministry, which had in a statement said assailants targeted his car and engaged in a gunfight with his bodyguards outside the capital.

Iran's foes had singled out Fakhrizadeh as a target "for twenty years", and an attack was anticipated to take place at some point, Shamkhani said.

"Security forces had predicted the possibility of an attack on him, even predicting the possible location of the incident," he said at the scientist's funeral in Tehran.

But given the "frequency of (such) news in these twenty years, the required seriousness was sadly not applied" this time, he added.

According to Iran's defence minister Amir Hatami, Fakhrizadeh was one of his deputies and headed the ministry's Defence and Research and Innovation Organization, focusing on the field of "nuclear defence."