Iranian officials and media have blamed both Israel, which Tehran calls "the Zionist regime," and the United States for Tuesday's killing of professor Massoud Ali-Mohammadi. Washington has dismissed the charge of U.S. involvement as absurd.
"The depth of the enemies' grudge can be seen in the university professor's assassination," Ahmadinejad said, ISNA news agency reported.
"The manner of bomb planting shows a Zionist style and they want to make sure that Iran would not advance," he said.
State media have said Ali-Mohammadi was killed by a remote controlled bomb on a motorcycle. When he was buried in Tehran on Thursday, the crowd chanted "Death to America" and "Death to Israel," state television reported.
Iranian officials have described the professor as a nuclear scientist but a spokesman said he did not work for the Atomic Energy Organization at the center of the Islamic Republic's disputed nuclear program.
"They don't want to see thinkers and scientists in Iran and do not want to see its development," Ahmadinejad said, referring to Iran's foes, IRNA news agency reported. "The enemies cannot take away the concept of genius from Iran by killing geniuses."
Ahmadinejad accused the West of seeking to dominate the Middle East, saying the September 11, 2001, attacks in the United States were used as a pretext to gain dominance over the region.
"The September 11 incident was very suspicious and complex … One could see it was like a funny show," Ahmadinejad said, according to the semi-official Fars news agency.
Tuesday's bombing — a rare attack in the Iranian capital — occurred at a time of heightened tension in the Islamic state, seven months after a disputed presidential election plunged the major oil producer into turmoil.
Iran has undergone its most serious domestic unrest since the Islamic revolution in 1979, as protests by opposition supporters against the election result have turned violent. Authorities say that election was the "healthiest" vote in the past three decades.
Eight people were killed in clashes between security forces and demonstrators on Ashura, the day of ritual Shi'ite mourning that fell on December 27 and opposition websites say more than 180 people have since been arrested.
A sister of Iran's Nobel Peace Prize Winner Shirin Ebadi, who was arrested after the December 27 protests, was released on Thursday, according to the website of al Jazeera television.
The bombing coincided with a sensitive time in Iran's dispute with the West over its nuclear ambitions, with major powers expected to meet soon to discuss possible new sanctions on Tehran over its refusal to halt its atomic work.
The West suspects Iran's nuclear work is aimed at developing bombs. Tehran says it wants only to generate electricity.
State media described Ali-Mohammadi as a "committed and revolutionary" professor, suggesting he backed the government.
However, the opposition website Jaras said he was an opposition supporter who backed moderate candidate Mirhossein Mousavi in last June's disputed election, which plunged Iran into turmoil.
(Writing by Fredrik Dahl; editing by Andrew Dobbie)
