Crime scene officials inspect the site of a bomb blast inside St Sebastian's Church in Negombo, Sri Lanka, on Sunday. File Photo/Reuters

Devastating Easter bombings in Sri Lanka were retaliation for attacks on mosques in New Zealand, a Sri Lankan official said on Tuesday, as Daesh claimed responsibility for the coordinated blasts that killed 321 people.

Daesh's claim, issued on its AMAQ news agency, came shortly after Sri Lanka said two domestic militant groups, with suspected links to foreign militants, were believed to have been behind the attacks at three churches and four hotels, which wounded about 500 people.

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Daesh gave no evidence for its claim. The government has said at least seven suicide bombers were involved.

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

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He did not elaborate on why authorities believed there was a link to the killing of 50 people at two mosques in the New Zealand city of Christchurch during Friday prayers on March 15. A lone gunman carried out those attacks.

Wijewardene said two Sri Lankan Islamist groups - the National Thawheed Jama'ut and Jammiyathul Millathu Ibrahim — were responsible for the blasts early on Sunday during Easter services and as high-end hotels served breakfast.

US intelligence sources said earlier the attacks carried some of the hallmarks of Daesh, even though it had not made an immediate claim of responsibility, as it usually does.

Prime Minister Ranil Wickremesinghe told parliament investigators were looking into foreign links.

Reuters