Cillian Murphy has heaped praise on 'Oppenheimer' co-star Florence Pugh for her helping to make their sex scenes "so f***ing powerful".

The movie features “prolonged full nudity” and sex scenes between J. Robert Oppenheimer (Cillian) - who spearheaded the development of the world's first atomic bomb - and his lover Jean Tatlock (Florence).

And Cillian, 47, says his 27-year-old castmate managed to make quite a "devastating" impact in the few scenes she's in.

He told The Sydney Morning Herald: “Those scenes were written deliberately.

“He knew that those scenes would get the movie the rating that it got. And I think when you see it, it’s so f***ing powerful. And they’re not gratuitous. They’re perfect. And Florence is just amazing."

The 'Peaky Blinders' star went on to hail Florence's acting as "f***ing phenomenal".

He added: “I have loved Florence’s work since 'Lady Macbeth' [William Oldroyd’s 2016 period drama about a woman embittered by a loveless marriage] and I think she’s f***ing phenomenal.

“She has this presence as a person and on-screen that is staggering. The impact she has [in 'Oppenheimer'] for the size of the role, it’s quite devastating.”

Director Christopher Nolan says the sex scenes - the first he's filmed in his career - were vital as Oppenheimer's "very intense relationship" with Jean, who is a Communist, and his "way with women" is a huge part of his story.

He explained to Insider: "Well, when you look at Oppenheimer's life and you look at his story, that aspect of his life, the aspect of his sexuality, his way with women, the charm that he exuded, it's an essential part of his story. His very intense relationship with Jean Tatlock, played by Florence Pugh, is one of the most important things in his life. But not least for the fact that Jean Tatlock was very explicitly a Communist and his obsession with her therefore had enormous ramifications for his later life and his ultimate fate. So it felt very important to understand their relationship and to really see inside it and understand what made it tick without being coy or allusive about it, but to try to be intimate, to try and be in there with him and fully understand the relationship that was so important to him."