At least 13 people were killed and more than 30 others were injured when a riot broke out at the Welikada prison.
The riot broke out when prison guards together with the police STF attempted to search the cells of the Welikada prison for heroin and mobile phones.
Irate prisoners then attacked the prison guards and police with stones forcing the police to fire tear-gas inside the prison to control the situation.
The situation however further escalated and the military was called in as the prisoners broke into the prison armory and stole the weapons.
The prisons department said that the prisoners had fired at the security forces and the police using the weapons they had stolen.
Eye witnesses said that some inmates had attempted to escape from the prison and were shot at by the security forces.
The Colombo national hospital said that 13 bodies were brought to the hospital and 34 others were admitted with injuries. Among those injured was the head of the STF.
A journalist who went to cover the riot was also injured and admitted to hospital. Police and army reinforcements were deployed to the prison and the situation as brought under control, the prisons commissioner said.