Natalie Portman was sexually terrorised as a child star

Natalie Portman has detailed how she was a victim of "sexual terrorism" at the age of 13 when shooting her first film.

At Saturday's Women's March in Los Angeles, the A-lister took the stage with fellow actress Eva Longoria to share her experiences of growing up as a child star.

"I turned 12 on the set of my first film Leon: The Professional, on which I play a young girl who befriends a hitman and hopes to avenge the murder of her family," she told the crowd.

"The character was spontaneously developing and discovering her womanhood, her voice and her desire. At that moment of my life, I too was discovering.

"I was so excited at 13 when the film was released that my work and my art had a human response and I excitedly opened my first fan mail to read a rape fantasy that a man had written me.

"A countdown was started on my local radio show to my 18th birthday - euphemistically the date that I would be legal to sleep with.

"Movie reviewers talked about my budding breasts in reviews. I understood very quickly, even as a 13-year-old, that if I were to express myself sexually I would feel unsafe and that men would feel entitled to discuss and objectify my body to my great discomfort."

The Oscar-winner explained how she changed the way she presented herself in public, rejecting roles which could sexualise her and building a reputation as "prudish, conservative, nerdy, serious".

"The response to my expression, from small comments about my body to more threatening deliberate statements, served to control my behaviour through an environment of sexual terrorism."

Portman was not the only award-winning actress to speak out at Saturday's march.

She was joined by her co-star Scarlett Johansson, who criticised those who have supported the cause only for it later to emerge they too have been sexual predators.

"My mind baffles - how could a person publicly stand by an organisation that helps to provide support for victims of sexual assault while privately preying on people who have no power," she said.

"I want my pin back, by the way."