Image copyright Getty Images Image caption In June police arrested three men after a young woman said she was threatened with penalties for breach of contract if she did not perform in porn films

A Japanese porn industry association has apologised and promised reform, amid allegations women are being forced to perform sex acts on film.

The Intellectual Property Promotion Association said it was "deeply sorry not to have taken any active action of our own volition".

It comes after an activist group warned women were being sexually mistreated in the industry.

Japan's adult sex industry has long been accused of human rights abuses.

Doubts about the criminal justice system are said to cause victims to hesitate coming forward.

In March, Human Rights Now, a Tokyo-based advocacy group, said it was aware of a rising number of cases in which young women hoping to be models were pressured to take part in obscene or pornographic videos.

'Breach of contract'

On Thursday, the IPPA, which represents video makers or labels, said after discussions with human rights lawyers it had come up with suggestions to govern the behaviour of production companies to try and prevent further abuse.

It said it would urge firms to make sure actresses agreed to take part in the video, and not force them to pay a penalty if they wished to cancel their appearance.

Earlier this month police arrested a former president of talent agency Marks Japan and two other men after a young woman said she was raped repeatedly on camera for adult videos.

She said she was threatened with financial penalties if she refused to perform sexual acts because it would be a "breach of contract".

Shihoko Fujiwara, a campaigner at a non-profit that helps victims of human trafficking, told AFP the statement was likely the first of its kind issued by the industry group.

But she pointed out that about 20% of adult film producers are not part of the association while some operations are underground.

"The remaining 20% and some illegal porn producers need to comply with the rules, which would require the government to take action," Ms Fujiwara said.