Syrian government troops have surrounded Hama prison and fired tear gas after inmates revolted, seizing several guards, a monitoring group reports.
The Syrian Observatory for Human Rights said inmates on Monday were protesting against a planned transfer of prisoners from Hama to Sednaya military prison, north of Damascus.
Those held in the Hama jail include political and Islamist prisoners, it said.
An insurgent group operating near Hama, located 210km from Damascus, said it was ready to shell government militias in towns nearby in response to mistreatment of the inmates, who it said were demanding "basic rights" including trial, the British-based Observatory reported.
The Ajnad al-Sham group said prisoners had urged the armed opposition to "break the siege" by government forces.
Insurgents later shelled Maharda, one of the towns Ajnad al-Sham threatened to attack, the Observatory reported.
It was not immediately clear if the shelling was linked.
An interior ministry official denied "reports from some media about Hama central prison", state news agency SANA said, without elaborating.
In August last year, hundreds of inmates at the prison rioted in protest against conditions and harsh sentences.
International rights groups say thousands of detainees are held in Syrian government prisons without charge and many of them are subjected to torture, a claim denied by the authorities.
