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, told state TV.

The People’s Mujahedeen of Iran (MEK) were “certainly” involved, along with “the Zionist regime and the Mossad,” he added, referring to Israel’s external security agency.

President Hassan Rouhani has stressed the country will seek its revenge in “due time” and not be rushed into a “trap.”

Israel says Fakhrizadeh was the head of an Iranian military nuclear program, the existence of which the Islamic republic has consistently denied, and Washington had sanctioned him in 2008 for activities linked to Iran’s atomic activities.

The scientist’s body was taken for a ceremony on Sunday at a major shrine in the holy city of Qom before being transported to the shrine of the Islamic republic’s founder Imam Khomeini, according to Iranian media.

On Monday live video from Tehran, shared by national outlet Iran Press, showed uniformed men gathering around images of Fakhrizadeh seemingly ahead of a procession.

His funeral will be held in the presence of senior military commanders and his family, the defense ministry said on its website, without specifying where.

Israel has not officially commented on Fakhrizadeh’s killing, less than two months before US President-elect Joe Biden is set to take office after four years of hawkish foreign policy under President Donald Trump.

Trump withdrew the US from a multilateral nuclear agreement with Iran in 2018 and then reimposed and beefed up punishing sanctions as part of its “maximum pressure” campaign against Tehran.

Biden has signalled his administration may be prepared to rejoin the accord, but the nuclear scientist’s assassination has revived opposition to the deal among Iranian conservatives.

The head of Iran’s Expediency Council, a key advisory and arbitration body, said there was “no reason why (Iran) should not reconsider the Nuclear Proliferation Treaty.”

Mohsen Rezai said Tehran should also halt implementation of the additional protocol, a document prescribing intrusive inspections of Iran’s nuclear facilitates.

Iran’s supreme leader Ayatollah Ali Khamenei called Saturday for Fakhrizadeh’s killers to be punished.

Parliament speaker Mohammad-Bagher Ghalibaf called Sunday for “a strong reaction” that would “deter and take revenge” on those behind the killing of Fakhrizadeh, who was aged 59 according to Iranian media.

For Israeli newspaper Haaretz, Fakhrizadeh’s killing was clearly tied to Biden’s arrival in office.

“The timing of the assassination, even if it was determined by purely operational considerations, is a clear message to President-elect Joe Biden, intended to show Israel’s criticism” of plans to revive the deal, it said.

The UAE, which in September normalized ties with Israel, condemned the killing and urged restraint.

The foreign ministry, quoted by the official Emirati news agency WAM, said Abu Dhabi “condemns the heinous assassination of Mohsen Fakhrizadeh, which could further fuel conflict in the region…

“The UAE calls upon all parties to exercise maximum degrees of self-restraint to avoid dragging the region into new levels of instability and threat to peace,” it said.

Britain, a party to the nuclear accord, said Sunday it was “concerned” about possible escalation of tensions in the Middle East following the assassination, while Turkey called the killing an act of “terrorism” that “upsets peace in the region.”

In Iran, ultra-conservative Kayhan daily called for strikes on Israel if it were “proven” to be behind the assassination.

Kayhan called for the port city of Haifa to be targeted “in a way that would annihilate its infrastructure and leave a heavy human toll.”

Iran has responded to the US withdrawal from the 2015 deal by gradually abandoning most of its key nuclear commitments under the agreement.

Rezai called on Iran’s atomic agency to take “minimum measures” such as “stopping the online broadcast of cameras, reducing or suspending inspectors and implementing restrictions in their access” to sites, ISNA news agency reported.

Iran’s parliament said the “best response” to the assassination would be to “revive Iran’s glorious nuclear industry.”

It called for International Atomic Energy Agency (IAEA) inspectors to be barred from the country’s atomic sites, said the legislature’s news agency ICANA.

Some MPs had earlier accused inspectors of acting as “spies” potentially responsible for Fakhrizadeh’s death.

But the spokesman for Iran’s atomic energy organization, Behrouz Kamalvandi, told IRNA on Saturday that the issue of inspectors’ access “must be decided on at high levels” of the Islamic republic’s leadership.