In this April 21, 2019, file photo, A Sri Lankan police commando enters a house suspected to be a hideout of militants following a shoot out in Colombo, Sri Lanka. Courtesy: AP Photo

Nearly a week after a series of blasts ripped through the island nation, Sri Lankan security forces killed four suspected Islamic State gunmen during an overnight raid, news agency Reuters reported. A civilian was also killed in the crossfire. The officials also discovered bodies of 15 people, including six children, during cleaning operations.

The gun battle near Sainthamaruthu in Ampara began Friday night after police tipped off soldiers to a suspected safe house, where militants set off three explosions and opened fire, the military said. At least three others were wounded in the attack, news agency AP reported.

Jayasekara said soldiers and police wanted to wait until daylight to carry out further raids given houses being built so close together. Meanwhile, the military says security forces have recovered explosives, detonators, “suicide kits,” military uniforms and Islamic State group flags during the raids.

The authorities are on a lookout for 140 people believed linked to ISIS, which claimed responsibility for the Easter Sunday suicide bombings that killed 253, as shooting erupted in the east during a raid. Nearly 10,000 soldiers were deployed across the Indian Ocean island state to carry out searches and provide security for religious centres, the military said.

President Maithripala Sirisena told reporters some Sri Lankan youths had been involved with ISIS since 2013. He said information uncovered so far suggested there were 140 people in Sri Lanka involved in ISIS activities. Around 70 are arrested, we will arrest them all very soon ending this (terror) he said.

ISIS provided no evidence to back its claim that it was behind the attacks. If true, it would be one of the worst attacks carried out by the group outside Iraq and Syria. The extremist group released a video on Tuesday showing eight men, all but one with their faces covered, standing under a black ISIS flag and declaring their loyalty to its leader, Abu Bakr Al-Baghdadi.

On Friday, security agencies continued searches and arrests in Colombo seizing explosives, weapons and suspicious vehicles as investigators struggled to find evidence on the emergence of local IS sympathisers in the country, the nature of their organisation and the origin of explosives used in the execution of one of the largest ever terror attacks in the recent past.