Natalie Portman says filming a sex scene with Mila Kunis for 'Black Swan' was "super awkward".

The beauty - who won an Oscar for playing Nina, a tortured ballerina in the Darren Aronofsky-directed movie - has previously acknowledged how difficult taking on the role was but has now revealed that the lesbian scene with her co-star was particularly unnerving to shoot.

She told the Australian edition of InStyle magazine: "It's super awkward. Anyone who tells you otherwise is not being honest. or they're a little off."

The 29-year-old star - who is expecting a baby with her fiance Benjamin Millipied, who was her choreographer in the film - also had to shoot some saucy scenes with Ashton Kutcher in comedy 'No Strings Attached' and acknowledges that casual sex is a frequent modern-day occurrence.

She explained: "I certainly have friends who could deal with that and others who could not. It's something I've seen in high-achieving women - they compartmentalize.

"You've got your work, your friends, your exercise, and your sex. You can tick off those boxes."