Australia’s onshore detention centres will be a focus of the Senate’s budget estimates hearings next month, following revelations of alleged mistreatment and complaint coverups within the facilities.

The federal opposition has called for the immigration minister to take seriously his duty of care for people in onshore detention centres.

Meanwhile, the Australian Greens have reiterated calls for a royal commission into Australia’s entire immigration detention system.

On Monday Guardian Australia reported on videos and audio filmed by detainees which revealed alleged use of excessive force by guards and a history of complaints being “shut down” by the operators, Serco.

The allegations were raised within a context of increasingly securitised conditions and growing mental health concerns after three men took their own lives in six months.

The independent senator for South Australia, Tim Storer, said: “The minister and his department ought to answer each and every complaint and question when Senate estimates deals with the portfolio on Friday week, rather than use the impending election as a smokescreen to avoid scrutiny.”

“It is not good enough for the government or the Department of Home Affairs to fend off specific queries about allegations of abuse with generic replies,” he said.

“[Serco] receives a great deal of taxpayers money to run these facilities and the voters should have confidence that their money is not being used to allow abuse of detainees.”

Guardian Australia’s investigation found:

guards had allegedly discouraged detainees from pursuing complaints

allegations of abuse and mistreatment of detainees

allegations by a former Serco employee that complaints were “covered up”

allegations that detainees had been arbitrarily transferred away from their home state

claims of “prison-like” conditions in detention centres

allegations of an increasingly militarised approach from authorities and rising tension within the centres

Shayne Neumann, the shadow minister for immigration and border protection, said the minister, David Coleman, had to take his duty of care seriously regarding detention and transit facilities on the mainland.

“This includes ensuring the health, safety and security of people detained in, working in, or visiting these facilities,” he told Guardian Australia.

“Australia’s onshore immigration detention centres are places of administrative detention – not punitive detention or correctional facilities.”

Neumann said Labor “shares the concerns of the wider community” about the management of the facilities over the past five years.

In one audio recording provided to Guardian Australia a Serco guard claims he has been the subject of numerous complaints which have never been investigated.

“I honestly have no idea how many complaints I’ve ever had,” the guard says. “You know how many times I’ve been investigated? Never.

“It just gets shut down just like that, because they know I’m doing the job I’m supposed to be doing.”

The independent MP Kerryn Phelps called for more transparency in the processes and conditions in detention and said “the culture of silence has to change”.

“The privatisation of detention centres appears to have resulted in a culture of impunity, with the government of the day often trying to offload any criticism to the contractor rather than take responsibility for people in our care,” she said.

The Greens immigration spokesman, Nick McKim, repeated calls for a royal commission into both onshore and offshore detention centres.

“People have been warehoused in prison-like conditions indefinitely, which has caused serious harm to them and their families,” McKim said.

“There has a complete lack of accountability and transparency of private companies who have made millions of dollars running a brutal regime. There is an urgent need for a robust, independent inspectorate of all Australian immigration detention facilities to ensure more humane treatment of detainees.”

Coleman’s office did not respond to requests for comment.

Previous inquiries to Serco were referred to the department of home affairs. Home affairs did not respond to a request for comment.