State media in Iran have accused Israel and the United States of being behind the killing of a nuclear scientist, who died in a bomb attack.
Masoud Ali Mohammadi, a professor at Tehran University, was killed when a bomb went off outside his home in the Iranian capital.
Media reports quote the Foreign Ministry as saying a preliminary investigation shows links to the US and Israel.
The United States says it's absurd to suggest that US agents were involved in the death.
Reports in the Iranian media described Mr Mohammadi as a nuclear physicist, but the BBC says it appears that his field of study was quantum theory.
No-one has claimed responsibility for the bombing.