The UN's top court on Thursday ruled that Syria must stop its torture program that investigators say killed tens of thousands, in the first international case over the brutal civil war that began in 2011.

The International Court of Justice said Syria must "take all measures within its power to prevent acts of torture and other cruel, inhuman or degrading treatment or punishment".

The court also ruled that Syria must "prevent the destruction and ensure the preservation of any evidence" relating to torture.

Canada and the Netherlands had called on the ICJ to "urgently" order a halt to torture in Syrian jails, arguing that "every day counts" for those still in detention.

"Today, the International Court of Justice recognized the urgency of the situation and the irreparable harm caused by Syria's recurring use of torture and other ill-treatment against its people," the governments of Canada and the Netherlands said in a joint statement.

The ruling comes after France issued an international arrest warrant for Syrian President Bashar al-Assad, accused of complicity in crimes against humanity over chemical attacks in 2013.

In October, judges at the ICJ in The Hague heard searing testimony from Syrian detainees describing gang rape, mutilation, and punishment involving contorting people into a car tire and beating them.

The court was asked to issue "provisional measures" to stop torture and arbitrary detention in Syria, open prisons to outside inspectors and provide information to families about the fate of their loved ones.

Torture in Syria is "pervasive and entrenched… and continues today", Canada and the Netherlands wrote in their submission to the ICJ.

Victims endure "unimaginable physical and mental pain and suffering as a result of acts of torture, including abhorrent treatment in detention… and sexual and gender-based violence", the submission added.

"Tens of thousands have died, or are presumed dead, as a result of torture," the two countries added, citing a report from the UN Human Rights Council.

Damascus snubbed the October hearing but has previously dismissed the case as "disinformation and lies" and said the allegations "lack the slightest degree of credibility".

"It is our sincere belief that the lives and well-being of Syrians are at stake and require the court's immediate attention," said Rene Lefeber, a top representative for the Netherlands, at the hearing on 10 October.

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.