The bodies of 15 people including six children were found after an explosion at a suspected Islamist militant hideout in east Sri Lanka, police said.
Police said the dead also included three women, believed to be family members of the suspected militants.
Residents said they heard an explosion followed by gunfire over several hours.
The clashes took place in Sainthamaruthu, not far from the home town of the suspected ringleader of the Easter Sunday suicide attacks.
Around the same time, security forces raided another building in a nearby town where they said they found explosives and a drone.
Sri Lanka has been on high alert since a co-ordinated wave of bombings last Sunday killed at least 250 people and wounded more than 500.
The bombings targeted churches which were packed full for the Easter holiday, as well as hotels popular with tourists.
Sri Lankan authorities blamed a local Islamist extremist group, National Tawheed Jamath, for the attacks, although the Islamic State group (IS) has also claimed it played a role.
Security forces have carried out raids across the country since the attacks, but officials say there are dozen of Islamic State sympathisers still at large in the country.
How did the raid unfold?
Police said the raid on Friday followed a tip-off about a location in a Muslim majority town of Ampara Sainthamaruthu, near Batticaloa.
An armed group at the location set off an explosion and a gun battle ensued, police said.
When troops moved in after dawn on Saturday they found 15 bodies in the burnt-out building, believed to be those of the suspected gunmen and family members, but also some civilians caught in the crossfire, police said.
The area is not far from the home town of radical preacher Zahran Hashim, the suspected ringleader of the attacks, who is said to have died in one of the bombings on Sunday.