Riots at Negombo Prison in western Sri Lanka left 26 people dead, including seven prison guards, and injured more than 100 over two days of violence.

The unrest began with clashes between inmate groups and escalated after prisoners reportedly seized guards’ weapons and attempted to storm the prison gates.

Security forces were deployed to restore order, while the violence was reportedly linked to a dispute over a drug trafficking operation inside the prison.

Authorities have launched an investigation and are transferring inmates to other facilities as relatives seek information about those affected, the BBC reports.

The incident is one of Sri Lanka’s deadliest prison riots in years and has renewed attention to the country’s severely overcrowded prison system.