A fourth X-Men' movie is in the works, but wage negotiations with some of the A-list cast are reportedly causing major headaches for bosses.

Executive producer Lauren Shuler Donner said: "The newer cast members are signed, and the older cast members are not."

Oscar winner Halle Berry - who played mutant Storm in the three previous X-Men films - recently revealed she would like to be involved in a fourth movie.

She said: "I would do it as long as I could. I've got some projects now that should keep me busy for the next two or three years if I'm lucky.

"It's a franchise that I love and a character that I love and now that I have a voice in the movie I really love it. If another great X-Men film came along I could probably change my plans."

Executive producer Donner has also confirmed that two spin-off projects from the highly successful comic book franchise are on schedule.

She explained: "Next, we're going to do Wolverine, but not before the end of the year as Hugh Jackman is working on a Baz Luhrmann film at the moment.

"We have the script and are working on it. We also have Young Magneto' in development."