Zoe Saldana and Sam Worthington are returning for the three 'Avatar' sequels.

The stars have signed on to reprise their characters Neytiri and Jake Sully for James Cameron's next three instalments of the sci-fi adventure, according to The Hollywood Reporter.

Cameron said: ''Jake Sully is a rare combination of passion, strength, street smarts and soul, which requires a lot from an actor. Sam brought to the role a combination of sensitivity, vulnerability and strength.

''Zoe captured every aspect of the character I envisioned, bringing to Neytiri a mix of delicacy, fierceness and incredible physicality. I am beyond pleased they'll be returning with us to Pandora.''

The deals come hot on the heels of Stephen Lang agreeing to returning for the upcoming movies - despite his character, evil antagonist Marine Colonel Quaritch, being killed off in the original 2009 movie.

It has also been revealed that interspecies couple Neytiri and Jake will have children, making it likely that they will no longer be the central characters for the latter movies.

Cameron is producing alongside Jon Landau, with Josh Friedman, Rick Jaffa, Amanda Silver and Shane Salerno working on the scripts.

Production begins this autumn in New Zealand, with the films scheduled for release in December 2016, 2017 and 2018.

'Avatar' was the highest-grossing film of all time, making $2.7 billion worldwide and winning three Academy Awards.