A university lecturer and nuclear scientist has been killed in a car explosion in north Tehran, reports say.
Iranian media sources named the casualty as Mostafa Ahmadi-Roshan, Reuters news agency reports.
The blast happened when a motorcyclist stuck a bomb on the side of the car, says Iran's semi-official Fars news agency.
Several Iranian nuclear scientists have been assassinated in Iran in recent years.
Tehran has blamed the killings on Israel and the US. Both countries deny the accusations.
Local sources said Wednesday's blast took place at a faculty of Iran's Allameh Tabatai university.
Two others were reportedly also injured in the blast, which took place near Gol Nabi Street, in the north of the capital.
Mr Ahmadi-Roshan, 32, was a graduate of oil industry university and supervised a department at Natanz uranium enrichment facility in Isfahan province, Fars reported.
The latest attack comes almost two years to the day since Massoud Ali Mohammadi, a 50-year-old university lecturer at Tehran University, was killed by a remote-controlled bomb as he left his home in Tehran on 12 January 2010.
Fars reports that the bombing method appears similar to another 2010 attack which injured former university professor Fereydun Abbasi-Davani, now the head of the country's atomic energy organisation.
There has been much controversy over Iran's nuclear activities.
Tehran says its nuclear programme is for peaceful energy purposes, but the US and other Western nations suspect it of seeking to build nuclear weapons.