Pirates of the Caribbean star Keira Knightley will appear partially nude for a racy scene in new movie Atonement.

Knightley will disrobe before plunging into a deep fountain and emerging soaking wet in a clingy slip. The film's director Joe Wright is quoted by Britain's Daily Express newspaper: "I wanted to cast Keira as a woman, a sexual character. She's only ever played girls before.

"There is a key scene with James McAvoy where she dives into a deep fountain to retrieve a broken vase. Keira emerges from the water and stands on the fountain's edge.

"It was her idea to stand there for quite so long - but I quite liked it."

Wright also claims the scene had to be edited to protect the 22-year-old actress' modesty.

He said: "There was another shot of her from behind but we left it out as it seemed a bit too rude." Keira has flashed her flesh in a number of previous films, including The Jacket, Domino and The Hole - in which she exposed her breasts.

She recently admitted she loves stripping naked in her movies and finds sex scenes "liberating". Keira is set to shoot an on screen threesome with Sienna Miller and Matthew Rhys in new Dylan Thomas biopic The Edge of Love.

She is currently on screen in the third Pirates of the Caribbean film, At World's End.