Police in Sri Lanka say 15 people, including six children, have died during a raid by Sri Lankan security forces as three cornered suicide bombers blew themselves up and others were shot dead.

The three men set off explosives killing three women and six children inside what was believed to an Islamist safe house near the eastern town of Kalmunai last night.

"Three other men, also believed to be suicide bombers, were found dead outside the house," police said in a statement.

Police backed by troops exchanged fire with those inside the house for over an hour, a military official said, adding that the bodies were recovered early this morning following a search operation.

A Military spokesman said gunmen opened fire on troops when they attempted to storm the house under cover of darkness, adding that a civilian had got caught in the crossfire and died.

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The joint operation was carried out following a tip-off that those responsible for the Easter suicide bombings were holed up in a built up area of Kalmunai, 370km east of Colombo, the capital.

Police said there were no casualties among the security forces.

The clashes came hours after the security forces raided a nearby location where they believe Islamist radicals recorded a video pledge to the leader of the so-called Islamic State group, Abu Bakr al-Baghdadi, before carrying out the Easter bombings.

Police said they found an IS flag and uniforms similar to those worn by the eight fighters for the video before they launched Sunday's attacks against three hotels and three churches, killing 253 people

The police said in an earlier statement last night: "We have found the backdrop the group used to record their video."

Islamic State released the video two days after the attack.

Police showed the clothing and the flag on national television, as well as some 150 sticks of dynamite and about 100,000 ball bearings seized from the house.

Security forces armed with emergency powers have stepped up search operations for Islamic extremists responsible for the bombings.