George Clooney is terrified Brad Pitt is planning to pull out of Ocean's 13.

Clooney - who is the main star of the latest instalment of the popular heist movies, as well as one of the producers - is reportedly furious with the'Troy actor because he hasn't signed the contract to star in the film.

Pitt - who has been living in Africa awaiting the birth of his first child with Angelina Jolie - is currently described as simply being "attached" to the movie.

Filming is due to start in two months and Clooney is reportedly getting increasingly desperate to get his best friend to commit to the project.

A source told Britain's The Sun newspaper: "Brad has not been able to confirm 100 percent that he will be available - and that's making George very anxious.

"His best friend is out of the country and looking forward to being a dad for the first time. But the movie is only weeks away now."

Pitt, 42, has barely been in the US since March - and has been spending quality time with Jolie and her two adoptive children in Namibia.

The source added: "Instead of being there to work on the project, Brad is in the middle of Africa. People are worried that he will prefer to carry on being a dad rather than go back to work."