In a speech at Fakhrizadeh’s funeral in Tehran, security chief Ali Shamkhani said the attackers “used electronic equipment” and were not present at the scene. He gave no further details.
The Iranian defence ministry initially reported that Fakhrizadeh was shot when several gunmen targeted his car.
Israel has not commented on the claims.
Fakhrizadeh played a crucial role in Iran’s nuclear programme in the early 2000s and more recently had been accused by Israel of continuing to help in the secret development of a nuclear weapon.
Iran insists that its nuclear activities are entirely peaceful.
The funeral ceremony for Mohsen Fakhrizadeh was held at the defence ministry in Tehran. His remains were then transferred to a cemetery in the north of the capital.
Iranian state television showed the flag-draped coffin being carried by troops, and senior officials – including Intelligence Minister Mahmoud Alavi, Revolutionary Guards commander Gen Hossein Salami and nuclear chief Ali Akbar Salehi – paying their respects.
Rear Admiral Shamkhani, the secretary of the Supreme National Security Council, told the ceremony that Iranian intelligence and security services had been aware of a plot to assassinate Fakhrizadeh, and that they had even predicted where the attack might take place.
“Necessary improvements were made for his security, but the enemy used completely new, professional and special methods and, unfortunately, they were successful,” he said.
He added: “It was a very complex mission using electronic equipment. There was no-one present at the scene.”
The admiral said there were “some clues” about the perpetrators’ identities, but that members of Mojahedin-e Khalq (MKO), an exiled Iranian opposition group opposed to clerical rule, were “surely” involved, along with “the Zionist regime and the Mossad” – a reference to Israel and its intelligence agency.
The comments came a day after Iran’s Fars news agency, which is linked to the Revolutionary Guards, reported that Fakhrizadeh was killed by a “remote-controlled machine gun”.
Arabic-language Al Alam TV meanwhile reported that the weapons used in the attack were “controlled by satellite”.
In the aftermath of Friday’s attack, Iran’s defence ministry had said that “armed terrorists” targeted Fakhrizadeh’s car in the town of Absard, to the east of Tehran, and that the scientist was fatally wounded during a gunfight between his bodyguards and the assailants.
Pictures on social media showed a road strewn with wreckage and blood, and a bullet-riddled car.
In his own speech at Monday’s funeral, Defence Minister General Amir Hatami reiterated Iran’s determination to avenge Fakhrizadeh’s killing.
“The enemies know, and I as a soldier tell them, that no crime, no terror and no stupid act will go unanswered by the Iranian people,” he said.
As head of Iran’s Organization of Defensive Innovation and Research, known by its Persian acronym SPND, Fakhrizadeh had carried out “considerable work” in the area of “nuclear defence”, the general said.
The government would double SPND’s budget in order to continue the path of the “martyr doctor” with “more speed and more power”, he added.
Israel’s Intelligence Minister, Eli Cohen, said on Monday in an interview with a radio station that he did not know who was behind the killing.
However, an unnamed senior Israeli official involved in tracking Iranian nuclear activities was quoted by the New York Times as saying that “Iran’s aspirations for nuclear weapons, promoted by Mr Fakhrizadeh, posed such a menace that the world should thank Israel”.
Israeli and Western security sources say Fakhrizadeh was instrumental in Iran’s nuclear programme.
The physics professor is said to have led “Project Amad”, a covert programme that Iran allegedly established in 1989 to carry out research on a potential nuclear bomb.
The project was shut down in 2003, according to the International Atomic Energy Agency (IAEA), though Israeli Prime Minister Netanyahu said in 2018 that documents obtained by his country showed Fakhrizadeh led a programme that was secretly continuing Project Amad’s work.
In a presentation, Mr Netanyahu urged people to “remember that name”.
Iran has previously accused Israel of assassinating four other Iranian nuclear scientists between 2010 and 2012.
Analysts have speculated that the latest assassination was not meant to cripple the Iranian nuclear programme, but rather to put an end to prospect of the US rejoining the 2015 Iran nuclear deal when President-elect Joe Biden takes office next year.
President Donald Trump abandoned the deal in 2018, saying it was “defective at its core”, and reinstated US sanctions in an attempt to force Iran’s leaders to negotiate a replacement.
Iran has refused to do so and retaliated by breaching a number of key commitments, including by increasing its stockpile of enriched uranium. Enriched uranium can be used to make fuel for nuclear reactors but also potentially nuclear bombs.
Source: News Agencies