Police say 15 people, including prison officers, were killed in the clash that broke out this morning (06) at Negombo Prison.
Among the dead are four prison officers and four inmates, according to reports.
Police and the Special Task Force have now entered the prison premises and brought the situation fully under control, our correspondent said.
More than 50 people, including prison officers, have been injured in the incident and admitted to hospital.
The Negombo Hospital stated that gunshot-related injuries were observed on the bodies of some of the deceased and injured.
The clash reportedly began following a coordinated attack carried out this morning by a group of inmates inside the prison, and security forces were forced to open fire to bring the situation under control.
The incident occurred after tensions inside the prison on the previous day (05) had been brought under control by midnight.
The clash between two groups of inmates at the Negombo Prison, which holds more than 1,800 short-term prisoners and remand suspects, began on the evening of the 5th.
Two inmates were killed and 34 others were injured in that earlier confrontation.
The violence is believed to have been triggered by an incident related to allegations of informing on a drug trafficking operation.
Subsequently, a group of male and female inmates staged a protest on the prison roof, and four inmates were injured and hospitalized after falling when a ceiling collapsed.
Police, the Special Task Force, and the Army were deployed to the prison last night to control the escalating situation.
Prison authorities say rioting inmates broke into the prison hospital and stole medication.
They also broke into the prison gymnasium and used iron bars found there during the violence.
However, amid fears that inmates might seize weapons during the unrest, prison officers removed firearms from the armoury last night.
Early this morning, inmates who had been calm resumed a coordinated attack on prison officers, assaulting them brutally and seizing mobile phones, according to reports.
Security officials say the attack was carried out in protest against strict prison controls.
Authorities also say 26 inmates linked to various criminal gangs are held at the prison.
Security sources say the violence was orchestrated by an inmate known as Katuwellégama Suresh, who is currently serving a prison sentence.
He is described as a close associate of Kehelbaddara Padme and faces charges including armed assault, robbery, and possession and trafficking of narcotics.
He is also accused of attacking a monk and his assistant at a temple in the Narammala area in 2016 and damaging a stupa after tying them up.
A case against him is currently being heard at the Negombo High Court.
He is presently in custody in connection with a case before the Negombo Magistrate’s Court.
