Syria has tortured tens of thousands of its people and maintains a "widespread and pervasive" system of "abhorrent treatment", world court judges heard on Tuesday at the first international case over the civil war.
Canada and the Netherlands have dragged Syria before the International Court of Justice, asking the court to demand urgent measures to stop the ongoing mistreatment of thousands still detained.
"Every day counts," Rene Lefeber, top representative for the Netherlands, told the court.
"Persons in Syria who are currently detained or at risk of being detained cannot afford to wait any longer," added Lefeber.
Damascus snubbed the hearing but has previously dismissed the case as "disinformation and lies" and said the allegations "lack the slightest degree of credibility".
Lefeber cited wrenching testimony from detainees, describing gang rapes, mutilation and a "standardised" punishment method involving contorting people into a car tyre and administering a "severe beating".
Canada and the Netherlands have asked the ICJ to "urgently" demand that Syria stop all torture and arbitrary detention, open prisons to outside inspectors and provide information to families about the fate of their loved ones.
The ICJ can take years to rule on a case but urgent so-called "provisional measures" can be ordered in a matter of weeks and are legally binding.
"It is our sincere belief that the lives and well-being of Syrians are at stake and require the court's immediate attention," said Lefeber.
Canada's main representative, Alan Kessel, said Syria had taken the "regrettable" choice not to appear but "this does not mean the world is absent".
"The Assad government must respond and stop the torture that is rampant in that country... We've held up a mirror to the Syrians. They should look in that mirror," Kessel told reporters, referring to Syrian President Bashar al-Assad.
Former prisoner-turned-activist Ahmad Helmi told AFP: "I was in prison in Syria for three years and I know for sure that torture is happening around the clock. It's happening around the hour."
"It doesn't happen only for interrogation. Sometimes it happens for fun, just because they feel they enjoy impunity. They can do whatever they want," he said.
"Hundreds of people are dying under torture every month," said Helmi in an interview before the hearing. A few dozen activists protested outside the court at the Peace Palace in The Hague.
Balkees Jarrah, from Human Rights Watch, said the ICJ needed to act "to prevent further abuses against Syrians, who continue to suffer under nightmarish conditions and whose lives are in serious jeopardy".
While there have been individual war crimes cases linked to the Syrian war in some countries, there has long been frustration in Western capitals at the lack of any wider plan for international justice.
The Dutch first launched a bid in September 2020 to hold Syria responsible for alleged breaches of the United Nations Convention against Torture, to which Damascus is a signatory.
Canada joined the case the following March.
The International Criminal Court (ICC) -- a war crimes court which, like the ICJ, is based in The Hague -- has been unable to deal with Syria because Damascus never ratified the Rome Statute, the tribunal's founding treaty.
The situation has gained renewed attention after the return of Assad to the international fold in May, when he attended an Arab League summit.
Describing the hearings as a "watershed" case, Human Rights Watch hoped the ICJ proceedings would shine a spotlight on Assad's return from isolation.
Activist Helmi said there was no chance of "rogue state" Syria accepting any decisions by the ICJ but insisted that any ruling was still important for victims and families.
"We are not talking about a local court somewhere. It's not me saying torture is happening. This will be the ICJ saying that torture is happening," he told AFP.
"And whoever wants to re-normalise the Syrian regime, they will have this tag on their forehead that you are normalising with a state that is torturing people around the clock."