An Iranian nuclear scientist has been killed by a bomb placed on his car in an attack a Tehran official blamed on Israel.
The victim, Mostafa Ahmadi-Roshan, was a professor at the Technical University in the capital and also supervised a department at the Natanz Uranium Enrichment Facility in central Iran.
Tehran blamed Israeli and US agents. Both countries deny the accusations.
Tehran's deputy governor Safarali Baratloo says Wednesday's bomb was a magnetic one - the same as those used in attacks on nuclear scientists in Iran a year ago, Reuters reports.
The Fars news agency quoted him as saying it was the work of the Zionists.
The bombing came as the United States sought to persuade a sceptical China to help efforts to toughen sanctions against Iran over its nuclear programme.
Tehran says its nuclear programme is for peaceful energy purposes, but the United States and other Western nations suspect it of seeking to build nuclear weapons.