Broken windows are seen at the family home of a bomber suspect where an explosion occurred during a Special Task Force raid, following a string of suicide attacks on churches and luxury hotels, in Colombo, Sri Lanka on Apr 25, 2019. (Photo: Reuters/Thomas Peter)

The shootout between troops and suspected militants erupted on Friday evening in Sainthamaruthu in Ampara, to the south of the town of Batticaloa, site of one of the Easter Sunday blasts at three churches and four luxury hotels.

A police spokesman said that three suspected suicide bombers were among the 15 dead after the shootout.

Military spokesman Sumith Atapattu said in a statement that as troops headed towards the safe house three explosions were triggered and gunfire began.

"Troops retaliated and raided the safe house where a large cache of explosives had been stored," he said in a statement.

He said the militants were suspected members of the National Towheed Jama'at (NTJ), which has been blamed for last Sunday's attacks.

The government has said nine homegrown, well-educated suicide bombers carried out the Easter Sunday attacks, eight of whom had been identified. One was a woman.

Police said on Friday they were trying to track down 140 people they believe have links with Islamic State, which claimed responsibility for the suicide bombings.

The police and military had earlier said four gunmen and a civilian had been killed in the shootout. The 15 were found in the morning during clearance operations.

The 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 the capital.

There were no casualties among the security forces, the police said.

The clashes came hours after the security forces raided the location where they believe radicals recorded a video pledge to Islamic State leader Abu Bakr al-Baghdadi before carrying out the deadly 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 luxury hotels and three churches, killing 253.

"We have found the backdrop the group used to record their video," the police said in an earlier statement on Friday night.

The Islamic State group had released the video two days after the attack.

Police showed the clothing and the flag on national television, as well as around 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./.

VNF/AFP