Actress Sienna Miller's appearance in Johnny Depp's much-anticipated James 'Whitey' Bulger biopic Black Mass has been cut.

The American Sniper star was cast as Catherine Greig, one of killer gangster Bulger's girlfriends, in the film, but director Scott Cooper has revealed he felt her storyline didn't fit into the movie.

He tells The Boston Globe, "It came down to narrative choices."

Miller talked about her role last year (14), admitting it was only a "cameo", but added she worked hard to get her Boston accent right for the part.

She said, "She (Greig) was quite a character from South Boston. The accent was something I really focused on because playing someone from Southie, you don't want to mess that up. Hopefully I've managed to pull that off, although I think everyone's like, 'How can you be English and think you can do that?'"

She continued, "I shot for two weeks... (and) I had an amazing time working with Johnny Depp, who I think is extraordinary, and Scott Cooper, the director, who's made some amazing films as well. The story's in the right hands and it was amazingly fun to come in... I got to age from 28 to 56."

Greig, who lived with the notorious crime boss for 16 years, was sentenced to eight years in prison for helping him evade capture from law enforcement officials.