A group known as the Hooded Men have won the latest stage of a legal battle to force an investigation into alleged torture by the security forces in 1971.
The Court of Appeal in Belfast dismissed an appeal by police against a ruling that detectives should revisit a decision to end their inquiry.
Fourteen men said they were subjected to torture after being held without trial in Northern Ireland.
The dismissal of the police appeal was a majority decision by the judges.
The Lord Chief Justice Sir Declan Morgan, Northern Ireland's most senior judge, said on Friday the treatment of the men "would, if it occurred today, properly be characterised as torture".
One of the three judges dissented with that conclusion.
Sir Donnell Deeny disagreed with Lord Chief Justice and Lord Justice Stephens on two matters.
He said it was not appropriate for the court to make a finding that the treatment is to be re-labelled as torture 48 years after the events and that he would find in favour of the PSNI chief constable, saying he was entitled to decide not to investigate further.
PSNI Chief Constable Simon Byrne said he wished "to acknowledge the distress this case has caused to many people over many years".
He added: "I note today's judgment and we will take time to consider the fullness of its implications and our next steps.
"We will now determine how best to progress this matter and meet our legal obligations. This case again brings into focus the need for a societal response to issues of legacy."
Several of the "Hooded Men" - who were interned without trial during the Troubles - are elderly and some have since died but nine are alive.
They say they were subjected to "deep interrogation" by the Army during their detention in Northern Ireland in 1971.
The men said they were forced to listen to constant loud static noise; deprived of sleep, food and water; forced to stand in a stress position and beaten if they fell.
They also said they were hooded and thrown from helicopters a short distance off the ground - having been told they were hundreds of feet in the air.
What happens now? BBC News Ireland correspondent Chris Page
Now the most senior judges in Northern Ireland have ruled in favour of the "Hooded Men", the onus is once again on the Police Service of Northern Ireland to respond.
There is an expectation amongst the men themselves that the police will appeal again and try to take this to the highest court in the UK - the Supreme Court.
But for now, the men are pleased they have won the latest stage in their legal fight.
They say they are determined to see the process through.
Francis McGuigan was 23 when he was taken for interrogation.
After Friday's ruling, he explained the lasting effect the experience had on him, saying he had been diagnosed with post-traumatic stress.
"What they had done to my brain and my body - I finished up that I couldn't spell my own name," he said.
"That is torture - it was torture then, it is torture today and it always will be torture and it has to be stopped throughout the world."
In 2014 the Police Service of Northern Ireland (PSNI) decided there was not enough evidence to warrant an investigation into the treatment of the internees in 1971.
But the PSNI's decision was quashed by a High Court ruling in October 2017.
That ruling followed a legal challenge in the High Court by the surviving members of the group, who wanted a new investigation into how they were treated.
Mr McGuigan said: "The High Court was right when it said there should be an investigation to identify and hold to account those ministers, Ministry of Defence and Royal Ulster Constabulary officers who were responsible for authorising and carrying out torture on us.
"I am pleased that the Court of Appeal has decided to uphold the ruling."
He added: "After waiting for justice for nearly five decades the time for accountability is long overdue".
Their case against the PSNI has been supported by the human rights campaign group Amnesty International.
Grainne Teggart from Amnesty International said the appeal court ruling was a vindication for the men's "fight for justice and offers hope for torture victims around the world".
"We must now urgently see an independent, human rights-compliant investigation into their torture, which was authorised at the highest levels of the UK government," she said.
"Those responsible for sanctioning and carrying out their torture at all levels must be held accountable and, where possible, prosecuted."
The case of the "Hooded Men" has been the subject of international legal action for more than 40 years.
In 1978 the European Court of Human Rights (ECHR) held that the UK had carried out inhuman and degrading treatment but fell short of defining that as torture.
In 2014 the Irish government said it would ask the ECHR to revise the 1978 judgement.
That was rejected by the ECHR in March last year.
The Irish government appealed the ruling that the UK did not torture the men - that appeal was rejected in September 2018.