Video report by ITV News Asia Correspondent Debi Edward
At least 15 people have died after Sri Lankan security forces carried out a raid on a safehouse used by the militants linked to the Easter Sunday bombings.
A shoot-out began on Friday night after police tipped off soldiers about a suspected safe house near the eastern Sri Lankan town of Sammanthurai.
At least three explosives were set off and multiple shots fired.
Police say six children are among the dead and at least three others were injured in the melee.
Police spokesman Ruwan Gunasekara said some of the dead will likely be militants who blew themselves up. One civilian is known to have died in the attack.
The government on Saturday formally banned two extremist groups purportedly linked to the attacks.
The ban on National Thawheed Jammath, or NTJ, and Jamathei Millathu Ibraheem, or JMI, allows officials to confiscate their property.
Police curfews are in affect around areas of east Sri Lanka and Catholic leaders have cancelled Sunday Masses indefinitely.
Muslims have also been warned to stay home amid fears there could be further attacks.
ITV News Asia Correspondent Debi Edward has the latest from Colombo, Sri Lanka
Security forces revealed they found explosives, detonators, "suicide kits", military uniforms. The discovery of a so-called Islamic State flag also gives the strongest indication yet that the group responsible for the nine bombings on Sunday is linked to the international terror organisation.
Following a tip-off from intelligence services, Mr Gunasekara said officers found 150 sticks of blasting gelatin and 100,000 small metal balls, as well as a van and clothing thought to have been used by those involved in the Easter attack.
Huge amounts of bomb-making material, including thousands of ball bearings, plastic explosives, chemicals and trigger devices which could be made into suicide vests were discovered in a house in Sammanthurai, sparking fears the Easter Sunday bombings could have been just the start of a massive terror campaign.
Despite Friday's raid, police say militants are still at large and have access to explosives, leading to increased security at places of worship across the country.
The grim discoveries come just hours after Sunday Masses were cancelled until further notice.
The Archbishop of Colombo, Cardinal Malcolm Ranjith said church officials had seen a leaked security document describing Catholic churches and other denominations as major targets for attackers.
He also asked the faithful to stay at home for their own safety.
"We don't want repetitions," said the cardinal in cancelling the services.
Cardinal Ranjith also appealed for financial support to rebuild the lives of affected people and reconstruct the churches targeted in the so-called Islamic State-claimed suicide bombings, which killed over 250 people on Sunday.
On Friday, authorities urged Muslims not to hold congregational prayers over fears they might be targeted.
However, several mosques did hold prayers under the protection of security forces.
Police are also providing patrols to protect Muslims who are fearful of reprisal attacks in the wake of the atrocity.
Local militants with ties to the so-called Islamic State group conducted a series of suicide bombings on Easter Sunday at churches and luxury hotels in and around Colombo and in the distant seaside village of Batticaloa, as well as three related bombings.
Sri Lanka has remained on edge since the deadly attacks as authorities have pursued suspects with possible access to explosives.
Earlier on 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 attacked.
Zahran appeared in an Islamic State video claiming responsibility for the coordinated assault, and authorities in both Sri Lanka and Australia confirmed links between IS and the attack.
Australia's Prime Minister said it had been confirmed that the Sri Lanka attackers were supported by the Islamic State group, which has claimed responsibility for the massacre.
The group has distributed a video of Zahran and others pledging allegiance to the withered caliphate.
Sri Lankan President Maithripala Sirisena told reporters that about 140 people had been identified as having links to the Islamic State group, and that the government has the capability "to completely control" IS activities in the country.
"We will completely control this and create a free and peaceful environment for people to live," he said.
Police said investigators had determined that the attackers' military training was provided by someone they called "Army Mohideen," and that weapons training had taken place overseas and at some locations in Sri Lanka's Eastern Province.
Police also said they arrested the operator of a copper factory who had helped Mohideen make improvised explosive devices and purchase empty cartridges sold by the Sri Lankan military as scrap copper.
Mr Sirisena blamed Sri Lanka's defense secretary, who resigned Thursday, and police chief, who he said would soon step down, for failing to share information from international intelligence agencies about the plot.
hops that should be open remain with their shutters down and streets that would normally be packed appear deserted.
Security warnings of potentially more attacks have spread fear and road blocks remain in place as police stop and search motorists and motorbike riders around the capital Colombo.
Security officials are still hunting for suspects and explosives that are unaccounted for.