Groups of Syrian activists have launched in recent days several online campaigns to document the names of those killed in Syrian prisons from 2011 to date.
Thousands of Syrian detainees are believed to have been killed inside regime prisons, said Syrian lawyer Bashir al-Bassam.
"The causes of death range from torture of all kinds to lack of medical care or complications from injuries, but the majority died under the brutal torture to which detainees are regularly and systematically subjected to" in Syrian regime prisons, he told Diyaruna.
The campaigns coincide with the regime's acknowledgement of the death of a number of its detainees, he said.
The Syrian government has begun issuing death notices for political detainees at an unprecedented rate in an effort to resolve the fate of thousands of missing Syrians.
Since the spring, it has been sending lists of their names to civil status departments to have their deaths registered.
The regime has so far issued death notices for 3,430 detainees -- 1,000 from Daraya, 750 from al-Hasakeh, 550 from Aleppo, 450 from the Maadamiyat al-Sham, 30 from Yabroud and 650 from Homs, al-Bassam said.
"Families can now obtain death certificates for those killed," he said, adding that "with these actions the regime is trying to close their files permanently with regard to the legal aspect relating to personal status".
According to the activists, the estimated number of detainees killed in regime prisons exceeds 10,000, al-Bassam said, noting that some groups put the number at 13,000 killed under torture.
Amnesty has previously said that more than 17,700 people were estimated to have died in regime custody across Syria between 2011 and 2015.
As many as 13,000 people also have been killed in Saydnaya prison between 2011 and December 2015, in utmost secrecy, according to Amnesty. Many other people at Saydnaya have been killed after being repeatedly tortured and systematically deprived of food, water, medicine and medical care.
"Activists outside Syria, especially those present in European countries, are communicating with the families of those killed under torture to file lawsuits against the perpetrators after the collection of evidence that confirms detention and death under torture and the location in which it occurred," al-Bassam said.