But they said they were holding out for a broad deal to free all of them and to allow international monitors into the prisons. They called for the United Nations Syrian envoy, Staffan de Mistura, and the global powers to push for the enforcement of Security Council Resolution 2254, which calls for the protection and release of detainees.

Otherwise, they said, they feared they could be killed or face other reprisals for the revolt.

General Taha told a delegation of prisoners that he had no control over other security agencies and might even be killed along with them, said Fahad al-Moosa, one of the lawyers. Mr. Moosa added that intelligence officials were preventing General Taha from getting his diabetes medicine sent into the prison.

“The regime is using the policy of starvation and subjugation and exhaustion of detainees’ health to break the prison,” Mr. Moosa said from an insurgent-held area where he runs a shelter for released prisoners. “After they take it over, they will start to torture these prisoners.”

Syria’s prisons, ranging from official ones like Hama Central Prison, the site of the revolt, to a network of sites controlled by secret police agencies and pro-government militias, are riddled with torture, arbitrary detention, overcrowding and a lack of food and medicine, according to numerous reports by Syrian and international human rights groups.

Opposition groups say that at least tens of thousands of people are now detained, with families often left in the dark for years about the prisoners’ location and condition.

One antigovernment monitoring group, the Britain-based Syrian Observatory for Human Rights, recently contended that according to government sources, at least 60,000 people had died in detention since the uprising against Mr. Assad began with street protests five years ago.

The government denies such allegations and says its prisoners are terrorists and other criminals.

Many other combatants — armed opposition groups, the Al Qaeda-linked Nusra Front, Islamic State militants and Kurdish fighters, to name a few — are holding prisoners and hostages, but plans for prisoner exchanges as part of the latest round of talks in Geneva never got off the ground.