Sri Lankan police say they exchanged fire with an armed group in the east of the country as they searched for those linked to last Sunday’s bombings.
A military spokesman said there was also an explosion as police conducted a raid in the town of Ampara Sainthamaruthu, near Batticaloa.
In a separate raid nearby, police said explosives and uniforms of the Islamic State (IS) group were seized.
Earlier, Sri Lanka’s PM said warnings of the attacks had not been passed on.
Ranil Wickremesinghe told the BBC he had been “out of the loop” and that vital intelligence warnings had not been passed to him.
The subsequent co-ordinated suicide bombings on three luxury hotels and three churches on Easter Sunday claimed at least 250 lives.
Sri Lanka has deployed nearly 10,000 security personnel across the country to track down all those responsible for the attacks and to provide security at religious sites.
Authorities have blamed a local Islamist extremist group, National Tawheed Jamath, for the attacks, although IS has also said it was behind them.
Security was stepped up around mosques for Friday prayers as some Muslims stayed away for fear of revenge attacks.
What is the latest?
In Ampara Sainthamaruthu on Friday, police said officers acting on a tip-off had launched a raid and that an armed group had set off an explosion. A gun battle then ensued.
Details were sketchy but Sri Lankan media said one civilian had died as well as several suspected militants.
In another raid in the same town police found IS uniforms, 150 sticks of gelignite, 100,000 metal balls and a drone camera, a military spokesman said.
Police quoted by local media said 10 arrests were made across the country on Friday bringing the number detained since last Sunday to 80.
President Maithripala Sirisena has told reporters that intelligence services believed about 130 suspects linked to IS were in the country and that police were hunting 70 who were still at large.
What is the political fallout?
Sri Lanka’s police chief and top defence ministry official have both resigned over the bombings.
But Mr Wickremesinghe argued that as he had not been aware of the warnings, he did not need to step down from his position.
“If we had any inkling, and we had not taken action, I would have handed in my resignation immediately,” he said, adding: “But what do you do when you are out of the loop?”
The breakdown in communication has refocused attention on the infighting between the country’s two most powerful men – Mr Wickremesinghe and President Sirisena.
Relations between the two deteriorated to such an extent that last October, Mr Sirisena sacked Mr Wickremesinghe. He was reinstated in December following rulings by Sri Lanka’s highest courts.
Who were the attackers?
Nine people are suspected of carrying out the attacks. President Sirisena confirmed that the alleged ringleader, Zahran Hashim, a radical preacher, died in the attack at the Shangri-La hotel in the capital, Colombo.
Two of the bombers are said to have been the sons of spice trader Mohammad Yusuf Ibrahim, one of Sri Lanka’s richest men. Mr Ibrahim was detained and questioned after the attacks.
One of his sons was reportedly the second bomber at the Shangri-La hotel alongside Zahran Hashim. The other son reportedly targeted the restaurant at the high-end Cinnamon Grand hotel, a short distance away.
A woman said to be a wife of one of Mr Ibrahim’s sons detonated explosives during a police raid at the family’s villa on Sunday. Several people, including children and three police officers, were reportedly killed in that blast.
According to the Sri Lankan government, most of the attackers were “well educated” and had come from “middle- or upper middle-class” families.
Another of the alleged bombers studied in the UK, a senior Whitehall official told the BBC. Abdul Latif Jamil Mohammed studied aerospace engineering at Kingston University in 2006-7 but did not complete a full degree.