Sri Lanka's President has outlawed two Islamist groups believed to be behind the suicide bombings on churches and hotels, while the wife and child of the suspected ringleader have been wounded during a military raid.
The National Thawheedh Jamaath (NTJ) and Jamathei Millathu Ibrahim are banned under President Maithripala Sirisena's emergency powers, Sirisena said in a statement on Saturday.
The announcement comes nearly a week after the Easter Sunday attacks, which killed more than 250 people.
Authorities could not act earlier to ban the two little-known groups because the law required them to show firm evidence against them, officials said.
Police believe the suspected mastermind of the bombings, Mohamed Hashim Mohamed Zahran, led either the NTJ or a splinter group.
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Less is known about Jamathei Millathu Ibrahim, whose members are also believed to have played a role in the bombings.
Islamic State has claimed responsibility for the attacks.
Nearly 10,000 soldiers have been deployed across the island to carry out searches and boost security since the bombings in three churches and four hotels, most of which were in the capital Colombo.
Security forces have detained 100 people, including foreigners from Syria and Egypt, police said.
A gun battle erupted on Friday evening during a raid on a safe house in Sainthamaruthu in Ampara district on the island's east coast, killing at least 15 people including three people with suicide vests and six children, a military spokesman said.
The wounded included the wife and a daughter of Zahran, his family said.
"Yes, the wife and daughter were injured in the attack," Zahran's sister Mohamed Hashim Mathaniya said.
"I was asked to come to identify them but I am not sure I can go," she told Reuters from the town of Kattankudy, where Zahran was originally based.
Zahran's driver was detained in a separate raid, according to a police statement.
Bomb-making materials, dozens of gelignite sticks and thousands of ball bearings were found in a search of a separate house in the same area, along with Islamic State banners and uniforms, the military said.
Zahran appeared in a video released by Islamic State days after the bombing, the only one showing his face while seven others were covered.
In the video the men stand under a black Islamic State flag and declare their loyalty to its leader, Abu Bakr Al-Baghdadi.
Authorities have said there could be more attacks against religious centres.
Sirisena and the government of Prime Minister Ranil Wickremesinghe have faced strong criticism after it emerged that India had repeatedly given warnings of the possibility of attacks.
Both Sirisena and Wickremesinghe have said intelligence was not shared with them, exposing rifts at the top of the government and raising questions about its ability to deal with the security crisis.
The national police chief had refused to accept Sirisena's request to step down, two sources told Reuters on Saturday, a further embarrassment for the president.