Australia's attorney general Christian Porter, came forward as the man named in an anonymous letter sent to politicians last week.

The letter alleged that Porter raped a woman in 1988 before he entered parliament.

It was referred to Australian federal police for a fresh investigation.

On Tuesday, police in the state of New South Wales, where the alleged assault occurred, said there was insufficient evidence to investigate the claim and closed the matter.

A previous investigation was suspended after the alleged victim committed suicide last year.

Porter denied that the alleged assault took place.

He said he had not had a sexual relationship with the woman involved.

Asked me that question.

The only thing that I can say likely the only thing that I'm ever going to be able to say and it's the truth and that is that nothing in the allegations that have been printed ever happened.

Yeah, even now the only information I have about the allegations is what has been circulating online and in certain media outlets if I stand down from my position, Porter went on to say that he would not resign from his ministerial position but would take leave for a couple of weeks to improve his mental health.

Earlier this week, Prime Minister Scott Morrison said he had spoken to the then unnamed minister, who had quote vigorously rejected the allegation circulated to.