"The President (Maithripala Sirisena) is planning to make some changes in the security establishments", he said. He did not say who would replace them.
The government has acknowledged it received warnings that a local extremist group was threatening churches.
Overnight, Sri Lankan police carried out fresh raids, detained 18 more people in their hunt for those involved in the attacks.
On Tuesday, in an address to Parliament, Wijewardene said "weakness" within Sri Lanka's security system had led to the failure to prevent the bombings.
The Islamic State claimed responsibility for Sunday's attacks, but Sri Lankan authorities said its role remained unclear. According to local authorities, numerous suicide bombers were educated and from wealthy families.
Speaking at a briefing on Wednesday, Deputy Defense Minister Ruwan Wijewardene said most of the attackers were "well educated" and came from "middle class" backgrounds.
Security sources have named him as Abdul Lathief Jameel Mohamed, Sky News reports.
"People question why action had not been taken despite the availability of intelligence support from a friendly neighbouring country", Sirisena said. His name was first reported by Sky News.
Ahead of launch, OnePlus 7, 7 Pro full specifications leaked
OnePlus fans can get entry vouchers for the launch event from 10am IST on April 25 via the OnePlus India website. However, OnePlus isn't speaking a lot about incorporating 5G capabilities into the phone, at least for now.
"Terrorists can strike without warning", Alaina Teplitz told reporters.
The militant group's news agency Amaq released a video showing eight terrorists said to be the perpetrators of serial bombing in Sri Lanka pledging allegiance to Abu Bakr al-Baghdadi, the leader of Daesh.
Sri Lankan Muslim leaders said they have also made many complaints to police about Hashim's activities in recent months. The emergency gives police and military extensive powers to detain and interrogate suspects without court orders.
The memo, translated to English by the New York Times, detailed how one of the members of the terror group National Thowheet Jama'ath, known as Mohammed Milhan, used social media to spread "hate speech against non-Muslims" following the Christchurch attacks, which killed 50 people. He said that one of the nine bombers was a woman.
On Wednesday, the United States envoy to Sri Lanka warned that there were "ongoing terrorist plots" in the country.
It is dominated by Sinhalese Buddhists but also has a significant Tamil minority, most of whom are Hindu, Muslim or Christian. The Tigers were crushed by the government in 2009.
Hundreds were killed and 500 injured in a series of coordinated blasts in churches and hotels, in Sri Lanka's deadliest violence since a devastating civil war ended in 2009. Its small Christian community has seen only scattered incidents of harassment.