A leaked Iranian memo suggests that Tehran was actively working on components of a nuclear bomb as recently as 2007.
Iran insists that its nuclear programme is for peaceful purposes.
The memo appears in a British newspaper, The Times.
The BBC reports it appears to be an internal Iranian technical document, that refers to a neutron source - uranium deuteride or UD3 - which experts say has no place in a peaceful nuclear programme and could only be related to weapons research.
