Arnold Schwarzenegger and Bruce Willis will take on "substantial" roles in 'The Expendables 2'.

The aging action stars took on cameo roles in the original movie written and directed by their friend Sylvester Stallone and both are to set to return in a significantly larger capacity for the sequel to the 2010 action film with Bruce set to play the main villain and Jean-Claude Van Damme his second in command while Arnold's role is as yet unclear.

They will join an all-star line-up including Jason Statham, Dolph Lundgren and Mickey Rourke with shooting set to begin in Bulgaria next week on the Simon West-directed movie.

David Varod, chief executive officer of NU Boyana studios, said: "It is going to be a sequel to the 'The Expendables'. The shooting is going to take place the second week of September. The movie is on, definitely. It will be a very good thing for Bulgaria, since there are some very big stars coming."

When asked who will star in the movie, he added: "Sylvester Stallone, Jason Statham, John Travolta, Arnold Schwarzenegger, Chuck Norris, Jean-Claude Van Damme, Dolph Lundgren, Mickey Rourke. Who else? Of course, Bruce Willis."

'The Expendables 2' - which will shoot in a variety of locations including Bulgaria and China - is due in cinemas in August 2012.