Actress Sienna Miller is set to star opposite Bradley Cooper in Clint Eastwood's upcoming movie `American Sniper`.

The 32-year-old actress is in early negotiations to take on the lead female role, opposite Bradley Cooper, in the upcoming film, reports contactmusic.com.

The film follows the story of an expert marksman who was killed by a discharged war veteran suffering from post-traumatic stress.

Shooting for `American Sniper` will begin in April.