President Bashar al-Assad has said that foreign Islamic State suspects could be tried in Syrian courts, raising the prospect the regime could use them as leverage against the West.
More than 10,000 Islamic State of Iraq and the Levant (Isil) fighters are currently in the detention of Western-backed Kurdish-led Syrian Democratic Forces (SDF) in north-east Syria, including 2,000 foreigners and at least seven Britons.
Thousands more foreign women and their children are also being held in camps across north-east Syria.
Assad made his comments in an interview with Paris Match magazine when asked about a deal with the Kurds that would eventually bring their areas under government control.
Abandoned by their US allies last month and facing an onslaught by Turkey, the SDF was forced to turn to the Syrian regime and Russia for protection.
"Every terrorist in the areas controlled by the Syrian state will be subject to Syrian law and Syrian law is clear concerning terrorism,” Assad said in a rare interview with a European news outlet. “We have courts specialised in terrorism and they will be prosecuted."
The Kurds have begun hearing the cases of local suspects in their makeshift courts but say they will not try foreigners, urging governments to take responsibility for them.
So far the UK and most other Western members of the international coalition against Isil have refused to repatriate their nationals from Syria, citing security concerns.
The Kurds have warned they cannot hold them forever.
Sources close to Damascus told the Telegraph that the fate of prisoners is being discussed as part of ongoing negotiations with the Kurds, who for the last five years have run an autonomous administration in the north-east in the absence of the government.
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The regime has regularly described the uprising against it as a foreign plot and could use the detainees as evidence of its claims.
Emma Beals, an independent Syria analyst, said this scenario would be a "win" for the regime: "(It) would then be in a position to attempt to extract concessions from the prisoner’s governments in return for their continued detention. The Assad regime has released jihadist prisoners to advance their perceived strategic aims in the past.
"It is a huge security risk, with dangerous individuals now at risk of release, or able to be used as bargaining chips against their governments,” she told the Telegraph.
Asked whether there was enough room to accommodate them in already overcrowded prisons, the source close to the regime said: “they’d make space”.
The British Government, which has so far taken back only a small number of orphans, has stripped many of its nationals in Syria of their UK citizenship and barred their return.
The UK has no diplomatic relationship with Damascus and so would not be able to formally object to the regime’s application of the death penalty.
Rights groups, however, fear that detainees may not even make it to court.
Tens of thousands have disappeared inside regime prisons since the start of the war in 2011. Thousands more have been executed without trial, while others have been tortured to death, according to Amnesty International.
The organisation has called the government’s most notorious prison, Sednaya, a “human slaughterhouse”.
“This would be a travesty and would obviously result in the deaths or disappearance of the prisoners for the most part, in patent violation of international law,” Clive Stafford-Smith, founder of Reprieve charity, told the Telegraph when the idea was first mooted.