Police in Sri Lanka say eight Tamil Tiger rebels have escaped from a jail in Batticaloa in the east.
The Tamil Tiger rebels have not commented on the incident
Prison staff told police the rebels were taking a morning wash when they pulled out a grenade.
However, one senior police official said there had been several jail escapes and officers were investigating whether the rebels had inside help.
Violence between rebels and the army has escalated this year, with more than 200 people killed in the past month.
Nihal Karunaratne, senior police official for Batticaloa district, said: "This is the third or fourth time prisoners have escaped from this jail. It was definitely an inside job.
"If our inquiry reveals prison people aided and abetted, they will be dealt with very severely and will be prosecuted."
The Tamil Tigers have yet to comment on the incident.
It comes amid international efforts to shore up the increasingly fragile 2002 ceasefire.