Aug 29, Colombo: At least seven prisoners were injured in an explosion inside the Batticaloa prison in eastern Sri Lanka early Friday morning, police said.

Police spokesman SSP Ranjith Gunasekara said a hand grenade exploded in one of the prison cells causing injuries to seven inmates. A second grenade was found in the prison by the Special Task Force police paramilitary unit, spokesman added.

All the injured were Tamils serving prison sentences for terrorist activities, the spokesman said.

The prison authorities have launched an investigation launched to determine how the grenade got smuggled into the prison.