CANBERRA – Save the Children has told an Australian Senate inquiry into allegations of physical and sexual assault at the Nauru detention centre that it had raised concerns about substandard conditions long before the Moss Review was released.

And the charity said its staff members in Nauru who were sacked by the Australian government have still not received an apology after a report claimed they had encouraged protests and self-harm as part of a wider campaign to embarrass the Australian government.

The Moss Review, ordered by a former Immigration Minister Scott Morrison to investigate the matter, found the claims had no substance.

It instead confirmed cases of rape, sexual abuse of children and the sale of drugs for sexual favours with some staff which led to the current Senate inquiry being instigated.

The inquiry, which comprises two Labor senators, one Liberal senator and a Greens senator, heard that asylum seekers on Nauru were being held in mouldy tents in temperatures above 30 degrees, and local guards were not screened for working with children.

The security company that has pocketed $1.2 billion for running the offshore processing centre on Nauru refused to address allegations of women being sexually abused on the island by their guards, or the conditions in which they are living.

Evidence presented on Tuesday included claims of guards trading cigarettes for sexual favours, and a woman being raped by a cleaner late at night on her way to the bathroom.

Representatives from security company Transfield Services avoided questions about the serious allegations.

Instead, Transfield said it was working on improving its “harassment and professional boundaries” policies.

“Despite our commitment and our best efforts, some allegations of misconduct have arisen,” said Kate Munnings, Transfield’s chief executive of operations.

Brett McDonald, the security contract manager for Wilson Security, which is contracted by Transfield, said he was aware of at least one incident in which a “transferee had been mishandled”, and “there have been some cases where staff have been moved on or terminated.”

Senator Kim Carr asked Wilson Security’s executive general manager, John Rodgers, about allegations that a woman had been raped by a cleaner while visiting a toilet at night.

“How is it that you are not able to maintain the security so that women cannot go to the toilet at night without fear of being assaulted,” Carr enquired.

“Senator, I don’t accept that we’re not able to maintain the security there. In the execution of our contract, we have consistently exceeded the KPIs that have been set for us and I believe we have done a very professional job of managing the security at the centre,” Rodgers replied.

A number of questions directed at the company were taken “on notice”, meaning they will be answered later, including on how many males and females worked at the centre.

The company could also not tell the committee what the gender breakdown was of its 275 expat guards and 277 local guards, how often there were power blackouts on the island, when it was first told of the allegations of rapes or sexual assault, or how often its “whistleblower hotline” was used.

The inquiry’s chair, Alex Gallacher, told Transfield’s Munnings, the lack of knowledge was extraordinary.

Munnings said: “Senator, we have come on short notice, we are very happy to participate, but we want to give the committee accurate information not guesses.”

Gallacher replied: “Absolutely. And if you’re asked the gender balance of 500 people I find it extraordinary that the three people at the table do not know. So take that on notice that I think that’s extraordinary.”

Greens immigration spokeswoman Sarah Hanson-Young said: “A seedy and toxic environment has been unveiled and it’s clear the government has been trying hard to cover it up.”

Australia’s immigration minister has called the inquiry a witch hunt.

The minister, Peter Dutton, has accused the opposition Labor and Green parties of inquiry delaying proceedings to prevent the department from presenting its evidence, as it would have been an “inconvenient truth for the parties’ witch hunt”.

He says the department will cooperate fully with the inquiry, but it should be seen as nothing more than a waste of time and taxpayers’ money.

Dutton says he has zero tolerance for criminal activity at detention centres, and the department has already made significant progress in implementing the recommendations of the Moss Review, which triggered the inquiry.

The Green Party senator Sarah Hanson-Young says the evidence being given raises serious concerns about the extent to which the immigration department knew women and children being had abused.

Meanwhile, Detention centres in Australia could be the focus of a national inquiry into child sexual abuse allegations.

Immigration authorities have been slapped with notices to hand over documents to the royal commission into child sex abuse.

This follows recent uncoverings of abuse at not only the detention centre on Nauru but also on the mainland and at the offshore camps on Manus Island and Christmas Island.