A university lecturer and nuclear scientist has been killed in a car explosion in Tehran.
Mostafa Ahmadi-Roshan, an academic who also worked at the Natanz uranium enrichment facility, and another unidentified person were killed in the attack.
The blast happened after a motorcyclist stuck an apparent bomb to the car.
Several Iranian nuclear scientists have been assassinated in recent years, with Iran blaming Israel and the US.
Both countries deny the accusations.
The BBC's Security Correspondent Gordon Corera is following the story.