The high court has upheld Australia’s right to send asylum seekers to offshore detention in Papua New Guinea, despite the PNG supreme court ruling the Australian-run processing centre on the island was “unconstitutional and illegal”.

The full bench of the high court, sitting in Brisbane, ruled Australia’s offshore arrangement with PNG was valid.

In the wake of the PNG court’s decision in April last year, lawyers in Australia challenged Australia’s role in offshore processing in the country, arguing it was not lawful for Australia to enter into an agreement that was not legal in another country.

But the high court found the Australian government was not constitutionally limited by the need to conform to the domestic law of another country, and the arrangement between the two nations was valid.

“The high court held that neither the legislative nor the executive power of the commonwealth is constitutionally limited by any need to conform to the domestic law of another country and that the past and future actions challenged by the plaintiff were not invalid or precluded,” the court’s judgment summary said.

The plaintiff in the case was Iranian asylum seeker Benham Satah, who has been held in PNG since August 2013.

Satah was a witness to the murder of Reza Barati in 2014 and was forced to give evidence in the trial of the two men who killed him, despite his initial refusal, because he had been threatened that he would be killed for speaking out.

Fearing reprisals over his evidence, he has refused to participate in PNG’s assessment of his asylum claim. Refugee status was denied to him last December.

Satah refuses to return to Iran, and that country does not accept its nationals being involuntarily returned, so PNG cannot deport him. Satah is currently in custody and could remain there indefinitely.

The immigration minister, Peter Dutton, said he remained committed to closing the Manus Island detention centre by the end of October but efforts to resettle people in America had been slowed by the US hitting its refugee “cap” for the year.

“We struck this deal with the United States,” he said. “We probably under the deal won’t get a lift of people now until October. I have stated very clearly that we want to close Manus Island facility by the end of October and we are on track to do that.

“If we can close Manus Island, then I think that is the closure of a sad chapter. One of the great things is, not only have we got kids out of detention, we have closed seventeen centres, but we have not had a death at sea.”

The Australian-run detention centres on Nauru and Manus Island were both reopened, under Labor, in 2012 and have been plagued since by allegations of violence, including murder; sexual predation of men, women and, in particular, children; medical neglect leading to death; high rates of suicide and self-harm; and other human rights abuses.

If we can close Manus Island, then I think that is the closure of a sad chapter. Peter Dutton, immigration minister

The US deal will not clear either of Manus or Nauru. Refugees in both countries say they are not safe living there. Both islands, but Manus in particular, have seen an upsurge of violence against refugees in recent months.

Challenge to mobile phone ban

In a separate court action in Australia, the full bench of the federal court asserted it did have jurisdiction to hear a challenge to a proposed government ban on mobile phones inside onshore immigration detention centres.

The government has been seeking to remove all mobile phones, citing security concerns.

The court ruled Thursday it could hear the class action challenge. The injunction previously granted to stop the government removing phones remains in place.

George Newhouse, principal solicitor at the National Justice Project, said the blanket removal of phones was deliberately cruel and part of the process of criminalising asylum seekers

“Peter Dutton claims that the use of mobile phones is linked to criminal behaviour but asylum seekers are not criminals,” he said. “Mobile phones are a lifeline to the outside world that enables them to maintain their sanity and communicate with their families, their loved ones, the community and their legal representatives.”

Concerns in parliament grow

And parliament remains seized on the growing concern around Australia’s offshore regime, highlighted by another death of an asylum seeker held on the island, Hamed Shamshiripour, whose body was found in bushland last week.

Following a speech from the Liberal party backbencher Russell Broadbent on Wednesday calling for the end of Australia’s offshore regime – “Enough. El Shaddai. Enough” – the independent member for Indi, Cathy McGowan, said she had been briefed by Dutton on the offshore situation, and that her constituents were deeply concerned by what was happening in the Australian run and financed centres.

McGowan told parliament the imminent closure of the Manus detention centre – without any resettlement plan for more than 800 men – has led to elevated stress levels on the island.

“While I totally get the logic of it, I don’t get the heart of it,” she said. “I don’t know how we as a nation can be so legalistic in our approach. Of course it’s important to follow the rules but to lose our heart, our care.

“I bring your call of the heart here to the parliament, I talk to my colleagues in the parliament, I say as a nation we are much better than this. We have a problem in Manus, we know we do.”

She said Australia needed to apply “Christian principles, love your neighbour as yourself.

“I stand in the House and say the Our Father, with my colleagues. I’m proud to be part of a Christian nation but I don’t see what we are doing in Manus is that.

“I think while we are forgetting that while the law is important, the heart is more important, and we need to hear that call of the heart of us as a nation, of my constituents – and I know every single member of parliament is hearing the same call.”

The Labor senator Lisa Singh told parliament Australia’s asylum policies had become an “international disgrace”.

“The rest of the world looks at our actions with dismay and disbelief, that we could treat people this way.”

Labor’s immigration spokesman, Shayne Neumann, said the government had failed to negotiate third-country resettlement for refugees.

“Russell Broadbent’s comments reflect the concerns of the wider Australian community about the Turnbull government’s failure to negotiate other third country resettlement options for refugees on Manus and Nauru.”

The Greens senator Nick McKim moved a motion in the Senate on Wednesday to compel the government to produce before parliament all documents and correspondence it has in relation to Shamshiripour, including details of his detention, requests for his transfer to Australia and incident reports about his condition and circumstances.

The Guardian revealed last week that the Australian Border Force’s chief medical officer, Dr John Brayley, was told more than a year before Shamshiripour’s death that he was suffering acute mental health problems, including psychotic episodes. Brayley, personally, and his office, received repeated correspondence about Shamshiripour’s deteriorating health and requests that he be moved.

Shamshiripour’s deteriorating mental health condition was reported by case managers and health professionals on Manus Island who said he had become a danger to himself and others.

McKim’s motion will be voted on on Thursday.