The riots in Welikada prison ended in a bloodbath, with 27 people dead and dozens injured.
Most of the dead were prisoners who were killed by armed police and army soldiers.
At least three prisoners were killed when they attempted to flee in an auto-rickshaw, which was shot at by security forces.
Clashes between prisoners and police erupted on Friday after a search operation was mounted. At least one prison guard was killed and several policemen and soldiers were injured during the violence.
Welikada prison has a history of violence against inmates, with clashes earlier this year leaving one Tamil prisoner dead.
Singhalese prisoners killed over 50 Tamil political detainees in Welikada during the Black July pogrom in 1983.
STF withdraws, SL army moves in with snipers - Welikada (09 Nov 2012)
Riots at Welikada prison after STF tries to search inmates (09 Nov 2012)