Natalie Portman found speaking Hebrew in her new film ''more challenging'' than she expected.

The Israeli-born actress is working on her directional debut 'A Tale of Love and Darkness', in which she also stars, and admitted she had to work hard to get her accent right because she kept making ''grammatical errors''.

She said: ''It was more challenging than I expected. I am pretty good but I still make a lot of grammatical errors, and I had to work a lot on my accent. It was okay to have an accent because my character in the movie is an immigrant, but it's not OK for her to have an American accent.''

The film - which is an adaptation of Israeli writer Amos Oz's memoir, set to be released next year - marks the first time the 34-year-old star has stepped behind the camera and although it was a huge task for the actress, she was comforted by Amos who only insisted nothing in the film was ''simplified'', especially his mother's suicide.

She told the Independent newspaper: ''Amos is an extremely kind, warm human being and so he didn't make me feel like I was on trial. I really had to show him my passion and commitment to the material and all he asked was that I don't make any sort of simplified explanations as to why she [his mother] killed herself. He said 'please don't do that'.''