Australia's scandal-hit government on Thursday apologised for calling an alleged rape victim a "lying cow," sparking fresh claims of a "toxic" culture in the country's corridors of power.

Prime Minister Scott Morrison said Defence Minister Linda Reynolds "deeply regretted" the slur against her former staffer Brittany Higgins, who last month came forward with claims of serious sexual assault.

"I spoke to Minister Reynolds this morning about this matter," Morrison said. "She knows those comments to have been inappropriate and wrong... they were made in her private office in a stressful week."

Higgins, 26, called the insult "incredibly hurtful" saying "that sort of behaviour and language is never excusable."

"It's just further evidence of the toxic workplace culture that occurs behind closed doors in Parliament House."

Australia's attorney general Christian Porter has denied that he raped a fellow student three decades ago
Australia's attorney general Christian Porter has denied that he raped a fellow student three decades ago AFP / Stefan Gosatti

It is just the latest in a series of revelations and allegations about the conduct of top officials in Canberra that have plunged Morrison's conservative government into a weeks-long rolling crisis.

Reynolds is just one of two senior cabinet ministers currently on health leave after being caught up in separate rape allegations.

Australia's attorney general Christian Porter is accused of raping a 16-year-old fellow student in 1988, an allegation he denies.

Reynolds is accused of mishandling Higgins' claim that she was raped in parliament by a colleague in 2019.

Morrison has backed both ministers to stay in their jobs, and on Thursday also rejected mounting calls for an independent investigation into the allegations against Porter.

Australia's Minister for Defense Linda Reynolds listens during a press conference at the US Department of State following the 30th AUSMIN on July 28, 2020, in Washington, DC.
Australia's Minister for Defense Linda Reynolds listens during a press conference at the US Department of State following the 30th AUSMIN on July 28, 2020, in Washington, DC. POOL / Brendan Smialowski

Porter was forced to come forward after senior lawmakers received a dossier setting out the claims of the alleged victim, who died last June without making a formal complaint to police.

The woman's family issued a statement on Thursday saying they "are supportive of any inquiry which would potentially shed light on the circumstances surrounding the deceased's passing," Australian media reported.

Her death -- reported to be suicide -- is the subject of an ongoing coroner's investigation.

Police said Thursday that after multiple contacts with the woman beginning last February, she told them the day before her death she "no longer felt able to proceed with reporting the matter, citing medical and personal reasons".

Morrison claimed any further inquiry would go beyond "the rule of law" as police had closed the case after finding, what they called, "insufficient admissible evidence" to proceed.

Morrison also insisted sacking Porter would create a precedent that put the rule of law at risk.

"There is not some other process. There is not the mob process. There is not the tribe-has-spoken process," he said.

There has been growing public outrage over the government's handling of sexual assault and harassment allegations.

Australia's parliament has been repeatedly criticised for a "toxic" workplace culture that has spawned persistent allegations of bullying, harassment and sexual misconduct against women in recent years.

Morrison said a new telephone support service has been set up for parliamentary staff and lawmakers who need counselling or support, as part of the government's response to the issue.