But questions have been raised about why Paladin was given the contracts after local media reported the firm had little experience, was thinly capitalised and had ties to a senior PNG politician.

The Australian Financial Review said Paladin’s registered office in Australia was a beach shack on Kangaroo Island, a sanctuary for native wildlife off the coast of South Australia.

After the reports surfaced last week, Paladin changed its registered address to an office in the capital Canberra, the newspaper reported on Monday.

Attorney general Christian Porter defended the decision to award the security contracts to Paladin, telling national broadcaster ABC the PNG tender “was the subject of a full independent Commonwealth procurement process”.

“I’m sure that the claims are going to be very thoroughly investigated,” he said of the reports challenging the size and process of the contract awards to Paladin. “The reality is that doing these types of things offshore in Papua New Guinea and in Nauru is a very costly exercise.”

But Porter added that reports of links between Paladin and the Manus-based family of a senior PNG politician would “have to be investigated thoroughly”.

Home Affairs Minister Peter Dutton, whose portfolio encompasses the offshore detention regime, last week distanced himself from the tender process which was reportedly closed, saying it was managed by lower-level officials.

Home Affairs officials are set to be quizzed about Paladin at parliamentary hearings on Monday and Tuesday, with opposition Labor Senator Murray Watt calling for transparency from the government.

“It’s about time they started providing some answers, about why A$400 million in taxpayer contracts can go to a company that no one has heard of, with no scrutiny about how the money is being spent,” he said.

Asylum seekers sent to Manus Island for processing were moved to the three centres when their camp was closed in late 2017 after a PNG court ruled it was unconstitutional.

Several security and service providers had previously walked away from running the contentious camps – which include one on the tiny island-state of Nauru – in the wake of domestic and international criticism of conditions at the centres, which rights activists and refugees have also complained about.

The Australian government last week announced it would reopen a detention centre on Christmas Island, claiming it anticipated a new wave of asylum seekers.

The opposition Labor party and independents voted to amend hardline immigration laws to give doctors the right to transfer some 1,000 men and woman from the Manus Island and Nauru detention centres if they need medical treatment.

The amendment, approved by the Senate on Wednesday, dealt a blow to the ruling conservative coalition which is trailing heavily in polls ahead of an election due in May. In response, Morrison offered a preview of a campaign pitch likely to focus on immigration.

“We have approved putting in place the reopening of the Christmas Island detention facilities, both to deal with the prospect of arrivals as well as dealing with the prospect of transfers,” Morrison told reporters in Canberra.

Previously, asylum seekers intercepted at sea and sent to camps in Papua New Guinea and Nauru were not allowed to set foot in Australia unless the government decided they need urgent care.

Additional reporting by Reuters