Hopkins plays a professor in The Human Stain

Port Talbot-born Hopkins plays professor Coleman Silk in the movie, opposite Nicole Kidman, Ed Harris and Gary Sinise.

The complex role sees Hopkins' life as a distinguished academic blown apart when it is revealed he is a light-skinned black man who has passed himself off as white in a deeply segregated society in 1940s America.

But the Oscar-winning star, who was full of compliments for Kidman, said he had not been tested playing the character.

"I read the book and the script and thought if they have faith in me, I'll keep it as simple as possible, learn my lines and leave it at that," he said

But director Robert Benton, who won Oscars for Kramer vs Kramer (1979) and Places in the Heart (1984), claimed Hopkins was not telling the truth.

"The enormous amount of work and energy that he put into this role is staggering," said Benton.

Nicole Kidman

"The risk he took, the courage it took for him to do this role is amazing."

Benton also praised Nicole Kidman as one of the "most accomplished actors" around.

"She is really a director's actor - whatever you want, she will do," he said.

Silence of the Lambs star Hopkins joined in giving plaudits for his co-star.

"She's lovely, she's beautiful to work with, very friendly and a wonderful actress," he said.

"If you work with someone who's really good and prepared, it's not really work, it's an enjoyable process."

The Human Stain, which is based on a novel by Philip Roth, is due to be released in the USA in September.