Human Rights Watch on Friday demanded unfettered access to Syrian prisons after a prominent peace activist died in custody and another was feared dead.
Omar Aziz, a 64-year-old husband and father of three, died of heart complications after he was transported to Harasta military hospital in the Damascus suburb of Mazzeh on Saturday, a relative told the watchdog.
Aziz, who returned to Syria from abroad in 2011 and began working with activists to deliver aid to embattled Damascus suburbs, was initially detained at his home on November 20 by armed air force intelligence agents.
A witness told HRW that Aziz was kept incommunicado in Mazzeh, where he was held in a small four-by-four metre (yard) cell with 85 others, exposed to cold temperatures, malnourished and told his family was imprisoned.
His family only learned he had died from one of his fellow detainees, the watchdog said.
Another activist Ayham Ghazzoul, 26, was also reported to have died by a recently released detainee who had been held with him at a military detention facility in the Damascus district of Kfar Susseh, it said.
The detainee said Ghazzoul died on November 9 from wounds suffered four days earlier when he was beaten by members of the loyalist National Students Union and two pro-regime militiamen who were transporting him to the facility.
"Aziz's death, and Ghazzoul's feared death are yet another reminder of the need to immediately lift the veil of secrecy over Syria's prisons," Sarah Leah Whitson, Middle East director at HRW, said in a statement.
"A constellation of abuse surrounds each incident of arbitrary detention in Syria, from the government's unwillingness to even acknowledge who is in their custody, to widespread torture and chilling reports of deaths in detention.
"The international community, and first and foremost Syria's allies, needs to bring pressure to bear on the government to stop these rampant abuses," Whitson said.
HRW has regularly documented pervasive violations by regime forces and officials, including arbitrary arrests and torture of peaceful protesters, humanitarian aid workers and doctors.
"The government should provide immediate and unhindered access for recognized international detention monitors to all detention facilities, official and unofficial, without prior notification," HRW said.
These monitors could include the office of the United Nations and Arab League peace envoy to Syria, Lakhdar Brahimi, and the UN Commission of Inquiry on Syria.