TEHRAN, Nov 28: Iran's top nuclear scientist Mohsen Fakhrizadeh was assassinated on Friday. He was the head of the Ministry of Defence's research and innovation organisation. He was said to be the brain behind Iran's nuclear weapons programme.

President Hassan Rouhani said Iran would retaliate. He accused "the mercenaries of the oppressive Zionist regime" (Israel) of killing the scientist. Iran's Supreme Leader Ayatollah Ali Khamenei called for 'punishment' of the "perpetrators of the attack." Khamenei's military adviser Hossein Dehghan vowed to "strike" the attackers like thunder.

A deal with six world powers had set a limit on Iran's production of enriched uranium in 2015. However, the US pulled out of the agreement in 2018. Enriched uranium is also used for making nuclear weapons.

The scientist was seriously wounded in the attack that targeted his car and an exchange of fire with his bodyguards in Absard, to the east of Tehran, on Friday. Fakhrizadeh later died in the hospital.

A professor of physics, Fakhrizadeh is said to have led Project Amad, the alleged covert programme that was established in 1989 to research the potential for building a nuclear bomb. It was shut down in 2003, but Fakhrizadeh continued it secretly. Suspicions that Iran was using the programme as a cover to develop a nuclear bomb prompted the EU, US and UN to impose crippling sanctions in 2010, according to the BBC.

The meeting between the Saudi Foreign Minister and Israeli Prime Minister last week has been suspect as motivated, targeting their arch enemy Iran.