James Cameron's futuristic 3D movie became the highest-grossing film of all time upon its release in 2009 and the only film in history to break the $2 billion mark.

Cameron had hoped to release the first sequel in 2014, but Landau admits the date is looking unlikely.

He tells Empire, ""We're not naming dates, but I think 2014 will be a tough date for us to make. It's about getting it right... movies make release dates; release dates don't make movies.""

The moviemaker is planning an Avatar trilogy, but is working hard to ensure the movies also stand alone as feature films, reveals Landau.

He adds, ""That's where movies fall into trouble - when they try to say: 'You know what? It's really one movie and there's an intermission' - so we want each one to be a stand-alone movie.

""The next one will kick off where the last one ended. But just like Avatar resolved itself and doesn't feel like a setup to another movie, you don't want Avatar 2 to feel like a setup for 3.""