The about two kgs of the narcotics consignment had returned after they failed to get delivered at the addresses given in Estonia, Canada, Russia and Sri Lanka.
The drug cache was intercepted by sleuths of the Delhi unit of the Narcotics Control Bureau (NCB) late yesterday.
According to sources, the NCB seized five parcels from Returned Letter Office (RLO) located in Jhandewalan containing a total of 715 gms of Heroin and 1.65kg of 'Charas'.
The NCB, which conducted the operation on specific inputs, is now looking for the people who had registered these parcels.
Officials said that the narcotics were being cleverly smuggled by concealing them in books and incense stick boxes.
"Further investigations are on," they said.