A Sri Lanka official says initial investigation shows Easter Sunday bombings were a retaliation against New Zealand mosque attack.

Photo: AFP

A series of coordinated blasts in churches and hotels hit Sri Lanka on Sunday leaving 321 people dead and 500 injured.

"The initial investigation has revealed that this was in retaliation for the New Zealand mosque attack," junior minister for defence Ruwan Wijewardene told parliament.

"It was done by National Thawheed Jama'ut along with JMI," he said, referring to another local group, Jammiyathul Millathu Ibrahim.

However, the Associated Press said Mr Wijewardene made the statement about retaliation "without providing evidence or explaining where the information came from".

A spokesperson for Prime Minister Jacinda Ardern said: "We have seen reports of the statement from the Sri Lankan Minister of state for defence, alleging a link between the the Easter Sunday terrorist attack and the March 15 attack in Christchurch.

"We understand the Sri Lankan investigation into the attack is in its early stages. New Zealand has not yet seen any intelligence upon which such an assessment might be based.

"New Zealanders oppose terrorism and extreme violence in all its forms. In the wake of the Christchurch mosque attacks, it was the condemnation of the perpetrators of violence and a message of peace that unified us all."

Meanwhile, Islamic State has now claimed responsibility for the bombings in Sri Lanka.

The news agency for the jihadist group, Amaq, has made the claim - but has not provided evidence supporting its involvement.

Members of the Sri Lankan government have previously said they believe the local Islamist group National Thowheed Jamath (NTJ) conducted the attacks but that they must have had international help.

Sri Lankan police detained a Syrian among 40 people being questioned about the Easter Sunday attacks, according to Reuters.

Tuesday was declared a national day of mourning and the funerals of some of the victims were held as pressure mounted on the government over why effective action had not been taken in response to a warning this month about a possible attack on churches by a little-known domestic Islamist group.

On 15 March, 50 people were killed in terror attack shootings at Al Noor Mosque and Linwood mosque in Christchurch.

- Reuters with RNZ