Colombo, Sri Lanka -- A series of explosions followed by a shootout between Sri Lanka's military and suspected Islamist militants erupted overnight, less than a week after suicide bombers unleashed a series of devastating attacks that killed more than 250 people on Easter Sunday.

A military spokesman said the militants are believed to be a part of the same group that carried out the Easter Sunday violence.

Special forces first raided a warehouse and discovered a huge cache of bomb-making equipment, including sticks of dynamite, detonator cable ball bearings and switches, CBS News' Elizabeth Palmer reports. They also found an ISIS flag. Police believe the site is where the Easter Sunday bombers may have made a video pledging allegiance to ISIS.

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A second raid in eastern Sri Lanka turned into a shootout with suspected extremists, who detonated three bombs inside a house, according to authorities. Officials say fifteen people were killed including three women and six children, presumed to be family members of the extremists.

Police spokesman Ruwan Gunasekara said some of the dead likely were militants who blew themselves up in suicide bombings.

Pictures showed survivors being treated at the scene.

A Sri Lankan girl is taken to a hospital after she was found at the scene on April 27, 2019. Achala Upendra/AP

The cruelty of last Sunday's hotel and church bombings have traumatized people on the island off the southern coast of India, and the recent raid that apparently shows extremists had planned further attacks is bound to amp up widespread fear.

"People are shocked, because this came years after the war ended, and after all these years, we have been living in peace," said 36-year-old Pradeep Kumara, a clerk at a private company, referring to Sri Lanka's long civil war that ended in 2009. "This has disrupted our work, and our ordinary and normal life. We don't want to go back to that troublesome period."

Officials from the police to the prime minister say militants remain on the loose and have access to explosives. That has led to increased security at shrines, churches, temples and mosques across the multi-ethnic country of 21 million.

Sri Lankan police and army soldiers secure the site after a gunbattle in Kalmunai, in eastern Sri Lanka, April 27, 2019. Achala Upendra / AP

Religious leaders have urged the faithful to stay home, fearing houses of worship are still targets.

Cardinal Malcolm Ranjith told journalists Friday that church officials had seen a leaked security document describing Roman Catholic churches and other denominations as a major target. He asked the faithful across Sri Lanka to stay home for their own safety and said: "We don't want repetitions."

It was an extraordinary request for a Catholic clergyman to make, as churches often remain a refuge. The U.S. Embassy in Sri Lanka has also warned the public to stay away from places of worship over the weekend -- a stark alert underlining that authorities believe that attackers remain at large.

Authorities also told Muslims to worship at home rather than attend communal Friday prayers that are the most important religious service of the week, but several mosques held services anyway. At a mosque in Colombo, Sri Lanka's capital, police armed with Kalashnikov assault rifles stood guard outside for hundreds of worshippers as the imam inside and others wept while praying to Allah to help their country.

Sri Lanka's government, crippled from a long political crisis between the president and prime minister last year, promised swift action to capture the militants still at large. President Maithripala Sirisena said about 140 people had been identified as having links to ISIS.

A "major search operation has been undertaken," Sirisena said. "Every household in the country will be checked."

Earlier Friday, police confirmed the militant group's leader, Mohamed Zahran, died in the suicide bombing at the Shangri-La Hotel, one of six hotels and churches that were attacked on Sunday. Zahran appeared in the ISIS video claiming responsibility for the coordinated assault, and authorities in both Sri Lanka and Australia confirmed links between ISIS and the deadly violence.