Snap protests were held across Australia on Saturday to rally in support of children held in juvenile detention facilities, as the fallout from the Don Dale centre revelations continues.

Following ABC’s Four Corners graphic investigation into the juvenile detention facility at Don Dale in the Northern Territory, a royal commission has been announced by the Australian prime minister, Malcolm Turnbull, to investigate how the events there were allowed to occur.

The footage published by the ABC of the use of teargas, spithoods and restraints has galvanised politicians into action and shocked Australians.

It has also sparked heavy international condemnation. Early on Saturday, the United Nations high commissioner for human rights, Zeid Ra’ad Al Hussein, released a statement saying the allegations could amount to torture.

“We are shocked by the video footage that has emerged from Don Dale youth detention centre in the Northern Territory in Australia, showing children as young as 10, many of whom are Aboriginal children, being held in inhumane conditions and treated cruelly,” a spokesman said.

“The treatment these children have been subjected to could amount to a violation of the Convention on the Rights of the Child and the Convention Against Torture and Other Cruel, Inhuman and Degrading Treatment, to which Australia is a party.”

The Northern Territory government has now suspended its use of controversial restraints within detention centres.

But on Saturday, the ABC reported that a Northern Territory MP, Nathan Barrett, had broken ranks and expressed his support for spithoods and restraint chairs.

The Warriors of the Aboriginal Resistance organised rallies across the country on Saturday in big cities across Australia, calling for an end to the detention of children.

Speakers across the country focused on the need for a broader national examination of the detention of Indigenous children.

The rally at Sydney Town Hall drew a crowd of about 400 people.

Aboriginal tent embassy founder Jenny Munro told the rally: “You can see once again how vulnerable our people are at the hands of the state.

“We need to understand the deep north and the deep west of this country. The racism in the territory and in the west is in your face every day.”

Indigenous elder Ken Canning said Indigenous Australians “knew it was happening all across the country”.

“Stop it now. Demand that all institutions holding our children be investigated immediately,” he told the crowd.

The NSW Greens MP David Shoebridge also addressed the crowd. He said the incarceration of Indigenous Australians was a national problem, and not just a Northern Territory one.

“They need to be released into the community and it needs to happen now,” he said. “The nation has known about this, our key decision makers have known about this for decades but haven’t taken action.”

“A young Aboriginal boy in New South Wales is 44 times more likely to be spending tonight in jail. This is a national shame. A national disgrace.”

In Melbourne large crowds also gathered at the State Library. Protests also occurred in Adelaide, Darwin, Canberra and Perth.

Dylan Voller, one of the juveniles who was held in Don Dale, issued a statement through his lawyers on Saturday calling for the protest to be peaceful.

“Dylan Voller has asked us to thank everybody for their demonstrations of support, however, he wants to send a special message to any protesters. Dylan wants all protesters to refrain from any violent or threatening behaviour,” the statement said.

“The protest organisers have been contacted and have agreed to relay Dylan’s message to the crowds.”

The protests come amid an expected apology from the federal indigenous minister Nigel Scullion at the Garma festival in Arnhem Land for being unaware of allegations of abuse.

Although the government acted swiftly to call the royal commission, there has been criticism of the process and the scope of the inquiry.

Indigenous leaders in the Northern Territory have expressed their disgust, saying the government failed to consult on the details of the commission.

The decision to appoint Brian Ross Martin as commissioner of the inquiry has also faced scrutiny, and some groups say the commissioner should have been a jurist from outside the territory.

The Northern Territory government has responded erratically to the coming commission. It has suspended its use of controversial restraints within detention facilities but MP Nathan Barrett later expressed his support for the measures.

On Saturday, the Indigenous affairs minister, Nigel Scullion, offered his own apology for not knowing of the abuses, despite being a long time senator for the NT and connected to its Indigenous communities.

“I am sorry that I was not fully aware of the circumstances that were exposed this week. Clearly, I must be better informed about such matters – particularly when the vast majority of youths held in detention in the Northern Territory are Indigenous,” he said.

“I commit to better monitoring of the actions of all state and territory governments – and I have already written to my counterparts in each government offering my support and seeking their advice about how we may do this.

Scullion said he was also sorry for accepting advice “indicating the Northern Territory Minister was responding to the concerns that were previously raised”.

He said there should be zero tolerance “for authorities entrusted with the welfare of children held in custody meting out brutality on these same children”, and called for the royal commission to identify both the failures of Don Dale and the causes of those failures.

He also rejected criticisms in reports which said he did not watch Four Corners until the prime minister told him to. Scullion said he had a “very private matter” which he honoured, and watched it later, and was horrified.

Earlier on Saturday, the chief minister Adam Giles arrived at the Garma festival in north east Arnhem Land, where the Don Dale abuses dominated many of the discussions.There has been talk on social media about attendees staging a protest by turning their backs on him, but academic and festival delegate Marcia Langton urged the crowd not to. She told the crowd to honour Aboriginal law, which dictated all guests invited to the land on which the festival was held would be treated with respect.