"I haven't really put pen to paper on it, but basically it goes back to the early expeditions of Pandora, kind of what went wrong with the humans and the Na'vi and what that was like to be an explorer and living in that world," contactmusic.com quoted Cameron as saying.
The 2009 sci-fi 'Avatar' is set in the mid-22nd century, when humans are mining a precious mineral called unobtanium on Pandora, a lush habitable moon of a gas giant in the Alpha Centauri star system.
Producer Jon Landau revealed earlier this year, that Cameron and crew will be shooting the second and third film back-to-back, with actors Zoe Saldana and Sam Worthington rumoured to be returning as lovers Neytiri and Jake Sully.
Cameron says he is keen to introduce some new characters.
"The only thing left to do is go back to see what it was like on those first expeditions and create some new characters that then become legacy characters in later films," said the 'Titanic' director.
Photos: Malaika Arora Khan in Bandra
Photos: Arjun Kapoor, Radhika Apte, Neha Dhupia at Mumbai airport
Photos: Aamir Khan, Amitabh Bachchan, other celebs at MAMI
Photos: Bipasha Basu, Preity Zinta, other actresses celebrate Karva Chauth
'Ae Dil Hai Mushkil' boys Ranbir, Karan on 'Comedy Nights Bachao'