Actors Amy Schumer and Ashley Judd have backed a campaign for an American woman convicted of killing a man who paid to have sex with her as a child to be given clemency.

Cyntoia Brown was 16 when she was convicted of murder and has been in prison in Tennessee since 2004.

She is not eligible for parole until 2059 and Democrats in Tennessee have asked the state's Republican Gov. Bill Haslam to offer her clemency before he leaves office in January.