Two assailants on a motorcycle attached magnetic bombs on Wednesday to the car of an Iranian university professor working at a key nuclear facility, killing him and wounding two others, a semiofficial news agency reported.
The attack in Tehran strongly resembles earlier killings of scientists working on the country's controversial nuclear program.
The bomb explosion killed Mostafa Ahmadi Roshan, a chemistry expert and a director of the Natanz uranium enrichment facility in central Iran, the semiofficial Fars news agency reported.
The killing of Roshan was similar to previous assassinations of Iranian nuclear scientists that Tehran has blamed on Israel and the United States. Both countries have denied the accusations.
Roshan, 32, was inside the Iranian-assembled Peugeot 405 car together with two others when the bomb expoded near Gol Nabi Street in north Tehran, Fars reported.
Fars described the explosion as a "terrorist attack" targeting Roshan, a graduate of the prestigious Sharif University of Technology in Tehran.
A similar bomb explosion on January 12, 2010, killed Tehran University professor Masoud Ali Mohammadi, a senior physics professor. He was killed when a bomb-rigged motorcycle exploded near his car as he was about to leave for work.
In November 2010, a pair of back-to-back bomb attacks in different parts of the capital killed one nuclear scientist and wounded another.
The slain scientist, Majid Shahriari, was a member of the nuclear engineering faculty at Shahid Beheshti University in Tehran and co-operated with the Atomic Energy Organization of Iran. The wounded scientist, Fereidoun Abbasi, was almost immediately appointed head of Iran's atomic agency.
And in July 2011, motorcycle-riding gunmen killed Darioush Rezaeinejad, an electronics student. Other reports identified him as a scientist involved in suspected Iranian attempts to make nuclear weapons.
Rezaeinejad allegedly participated in developing high-voltage switches, a key component in setting off the explosions needed to trigger a nuclear warhead.
The United States and other countries say Iran is trying to develop nuclear weapons technology. Iran denies the allegations, saying that its program is intended for peaceful purposes.