Director Roman Polanski is facing a civil trial in the US after being sued by a woman who has accused him of raping her at his home when she was under 18 in 1973.

The claim was aired in a news conference led by well-known US lawyer Gloria Allred. The claimant also appeared but did not give her name and was introduced as Jane Doe.

"It took me a really long time to decide to file this suit against Mr Polanski, but I finally did make that decision," she said. "I want to file it to obtain justice and accountability."

Polanski, now 90, has strenuously denied the woman's allegations and says the lawsuit is unconstitutional.

The filmmaker is still facing a separate unresolved criminal sexual assault case in Los Angeles after pleading guilty to one count of unlawful sexual intercourse and then leaving the country before a sentencing hearing in 1978.

In the civil lawsuit made public on Tuesday, the woman making the allegations said she went to dinner with Polanski, who knew she was under 18, in 1973, months after meeting him at a party.

She said he gave her tequila shots at his home beforehand and at the restaurant, and that she became groggy and he drove her home. She claims she then remembers lying next to him in his bed.

"He told her that he wanted to have sex with her," the lawsuit says. "Plaintiff, though groggy, told Defendant 'No.' She told him, 'Please don't do this'. He ignored her pleas. Defendant Polanski removed Plaintiff's clothes and he proceeded to rape her causing her tremendous physical and emotional pain and suffering."

At the news conference, Ms Allred said the woman was under 18 at the time but did not confirm her exact age, saying she would "be more specific at the appropriate time in this lawsuit".

"It took me a really long time to decide to file this suit against Mr Polanski, but I finally did make that decision," she said. "I want to file it to obtain justice and accountability."

Polanski, now 90, has strenuously denied the woman's allegations and says the lawsuit is unconstitutional.

The filmmaker is still facing a separate unresolved criminal sexual assault case in Los Angeles after pleading guilty to one count of unlawful sexual intercourse and then leaving the country before a sentencing hearing in 1978.

In the civil lawsuit made public on Tuesday, the woman making the allegations said she went to dinner with Polanski, who knew she was under 18, in 1973, months after meeting him at a party.

She said he gave her tequila shots at his home beforehand and at the restaurant, and that she became groggy and he drove her home. She claims she then remembers lying next to him in his bed.

"He told her that he wanted to have sex with her," the lawsuit says. "Plaintiff, though groggy, told Defendant 'No.' She told him, 'Please don't do this'. He ignored her pleas. Defendant Polanski removed Plaintiff's clothes and he proceeded to rape her causing her tremendous physical and emotional pain and suffering."

At the news conference, Ms Allred said the woman was under 18 at the time but did not confirm her exact age, saying she would "be more specific at the appropriate time in this lawsuit".