Australia's Attorney General Christian Porter has identified himself as the cabinet minister at the centre of a rape accusation - an allegation he strongly denies.

A letter sent to Prime Minister Scott Morrison last week alleged Mr Porter raped a 16-year-old girl in 1988. The woman took her own life last year.

New South Wales Police have closed their investigation into the matter.

Mr Morrison has previously rejected calls for his minister to stand down.

Mr Porter, 50, said on Wednesday: "The things that are being claimed did not happen.

"Nothing in the allegations that have been printed ever happened," he told reporters in Perth.

Mr Porter said he had the prime minister's "full backing" and would not step down from his position, but would take two weeks of leave.

Australian media had widely reported the allegation since last Friday without identifying Mr Porter, saying only that it involved a cabinet minister.

The alleged victim reported her complaint to New South Wales Police last year but did not make a formal statement. The investigation was suspended after she died last June.

On Tuesday, police confirmed they were dropping their investigation because there was "insufficient admissible evidence to proceed".

Sexual assault cases in Australia typically require an alleged victim's testimony to proceed with prosecution. That is not possible in this instance because the woman has died.

Mr Morrison's government has faced calls for a separate, independent investigation into the allegations.

Mr Porter argued that was unnecessary - he said he had never been contacted by police or other parties on the "substantive detail" of the allegations.

"If I stand down from my position as attorney general because of an allegation about something that simply did not happen, then any person in Australia can lose their career... based on nothing more than an accusation that appears in print," he said.

Mr Porter has been the nation's attorney-general since 2017 and is currently the government leader of the House of Representatives.

As the chief law officer of the nation, he controls one of the most senior government portfolios and is responsible for legal affairs, national and public security.

The government has been rocked by a wave of sexual assault allegations in the past fortnight.

Brittany Higgins, 26, a former aide to two government ministers, alleged she had been attacked by a male political adviser in 2019. She had later felt pressured to stay silent or risk losing her job, she added.

Her account has inspired other women in politics to come forward with allegations.