President Shimon Peres on Thursday denied that Israel was involved in the killing of a nuclear scientist in Iran on Wednesday.

During an interview with CNN, Peres was asked whether Israel was involved in the killing of a university professor and department head of a uranium enrichment facility in Tehran to which he answered: “Not to the best of my knowledge.”

“I know that it is fashionable that whatever wrong happens in Iran, it is the United States and Israel. There is nothing new in this approach,” said Peres.

Iran’s top cleric has blamed the CIA and Mossad, Israel’s intelligence agency, for killing an Iranian nuclear scientist, Iran’s state broadcaster said.

Mostafa Ahmadi Roshan, who died Wednesday, was the third Iranian nuclear scientist in two years to be killed by what Iran described as a magnetic bomb attached to his car. A fourth survived a similar assassination attempt.

Roshan’s death shows that “the global arrogance spearheaded by the U.S. and Zionism has reached a deadlock in confrontation with the determined, devout and progressive nation of Islamic Iran,” Supreme Leader Ayatollah Ali Khamenei was quoted as saying by the state-run Press TV.

Those responsible will not own up, Khamenei said, but the attack “has been carried out by the planning or support of CIA and Mossad [spy] services, like all other crimes of the network of international state terrorism.”

Khamenei ended his message of condolence with a warning: “We shall persist in punishing the perpetrators of this crime, as well those supporting them behind the scenes.”

Iran’s President Mahmoud Ahmadinejad sent his condolences Friday to the families of Roshan and his driver, who also died following the attack, the state-run IRNA news agency reported. He pointed the finger at “agents of imperialism and international Zionism,” a reference to Israel.

Other Iranian officials also blamed the killings on Israel and the United States, both of which have accused Tehran of pursuing a nuclear bomb — a claim it denies.

U.S. Secretary of State Hillary Clinton “categorically” denied any role in the attacks, but urged Iran to halt its quest for a nuclear bomb.

Defense Secretary Leon Panetta reiterated that message Thursday, telling troops in Texas: “We were not involved in any way — in any way — with regards to the assassination that took place there.

“I’m not sure who was involved, we have some ideas as to who might be involved… but I can tell you one thing: the United States was not involved in that kind of effort, that’s not what the United States does.”

Brig. Gen. Yoav Mordechai, a spokesman for the Israel Defense Forces, said on his Facebook page Wednesday: “I have no idea who targeted the Iranian scientist but I certainly don’t shed a tear.”

READ MORE: CNN