He said the militants were suspected members of the National Towheed Jama'at (NTJ), which has been blamed for last Sunday's attacks.
Amidst fears of new attacks, the Roman Catholic church has suspended all public services across the country until security is guaranteed by the government.
Police said Hashim's widow and their child were wounded in the Kalmunai raid.
Just days after the co-ordinated suicide attacks, Sri Lankan MP Professor Ashu Marasinghe called for the burqa to be banned across the country to prevent male and female terrorists using it to cover up their identity.
It said the militants were targeting five locations for attacks on Sunday or Monday.
The authorities have detained more than 100 people, including foreigners from Syria and Egypt, since the bombings in three churches and four hotels, most of which were in the capital.
Hashim, who blew himself up at a hotel in Colombo, founded an Islamist group, the NTJ, which authorities have said was behind the attacks.
"I come to this church every Sunday".
Three of the 15 people killed were the same people who were seen in the undated video on social media, in which they discus martyrdom and urge their followers to kill all non believers, police sources said.
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Police suspect the bombings were carried out by two local Islamist groups, including the one established by Zahran.
A girl and a woman survived the explosion but were critically injured and being treated at a hospital, police spokesman Ruwan Gunasekara said.
Another raid in the region targeted a house where authorities said Hashim and the other suicide bombers filmed a pledge of allegiance to IS before staging their attacks.
Video on state television showed explosives, a generator, a drone and a large quantity of batteries inside the converted studio.
The National Thawheedh Jamaath (NTJ) and Jamathei Millathu Ibrahim were banned under his emergency powers, President Maithripala Sirisena said in a statement, almost a week after the Easter Sunday attacks that killed more than 250 people.
In a statement on his official Twitter account, Wickremesinghe said: "We take collective responsibility and apologize to our fellow citizens for our failure to protect victims of these tragic events".
Only a small number of women are thought to wear the face-covering niqab, or the burka - a one-piece veil that covers the face and body.
The Sri Lankan Prime Minister had earlier accepted that some fundamentalists could not be arrested for their links with ISIS in absence of a law to deal with them in the country.
Sri Lankan army personnel search people and their bags at a checkpoint in the village of Kattankudy in Batticaloa, Sri Lanka, on Sunday.