Insight - Enigmatic Iranian military man at centre of U.N. nuclear investigation

VIENNA (Reuters) - He is believed to top the list of elusive Iranian officials the U.N. nuclear watchdog wants to query. Exiled foes of the Islamic state cite him as the mastermind of clandestine efforts to design an atomic bomb. Tehran is mum about him, while denying having any nuclear arms agenda.

Probably living under tight security, Mohsen Fakhrizadeh did not join this week's talks in Vienna between Iran and six world powers directed at striking a deal by late July to end a decade-old dispute over Tehran's nuclear aspirations.