Sri Lanka's Prime Minister warns more explosives 'out there'

The Sri Lankan Prime Minister has warned there are more militants and explosives "out there", following the devastating Easter Sunday bombings.

On Sunday, more than 320 people were killed when a series of explosions went off at churches and hotels across the country.

While evidence is scant, Islamic State has claimed responsibility for the attacks. The Government has said at least seven suicide bombers were involved.

At a news conference on Tuesday night, Sri Lanka Prime Minister Ranil Wickremesinghe warned there were more militants and explosives "out there" and officials would follow up the Islamic State's claims.

"We will be following up on Isis's claims, we believe there may be links," he said.

It comes as the country's President, Maithripala Sirisena, said the heads of the defence forces would change following their failure to act on intelligence that reportedly warned of a possible attack.

One prior warning reportedly said the Indian embassy was a possible target.

Questions are also being raised over which Government officials were aware of the intelligence report.

Meanwhile, emergency powers remain invoked in Sri Lanka, allowing the police and military to detain and interrogate suspects without the need for court orders.

On Tuesday, the Sri Lankan Minister of Defence said the attacks were retaliation for the Christchurch shootings. However, Prime Minister Jacinda Ardern said New Zealand officials had yet to see any intelligence to corroborate that assessment.

The Guardian reported an intelligence memo circulated to some in the Sri Lankan government in the weeks before the attack said one suspected perpetrator of the attacks had started to update his social media accounts “with extremist content” in the aftermath of the Christchurch shootings.

But terrorism researchers say the attack would have required months of preparations and were likely started before the events of March 15.

The first Sri Lankan explosion hit St Anthony's Church around 8:45am on Sunday (local time) as the Easter Mass took place, according to local journalist Roel Raymond.

Minutes later, another explosion ripped through St Sebastian's Church and the Zion Evangelical Church in Batticaloa, before three hotels were reportedly attacked - the Kingsbury Hotel, Shangri-la Hotel and Cinnamon Grand Hotel in Colombo.