Islamic State has claimed responsibility for the Easter bombings in Sri Lanka that killed more than 300 people, the group’s Amaq news agency has said.

The terrorist group gave no evidence for its claim on Tuesday, and has made a series of false claims in recent years. However, experts have said the suicide bombings of three churches and three luxury hotels bear the hallmarks of the group.

Earlier, Sri Lanka’s defence minister, Ruwan Wijewardene, said the attacks were a response to the recent mass shooting of Muslim worshippers in Christchurch in New Zealand.

“The preliminary investigations have revealed that what happened in Sri Lanka was in retaliation for the attack against Muslims in Christchurch,” Wijewardene told a special sitting of parliament, referring to the terrorist attack by a white supremacist in March in which 50 people were killed. The minister did not present any evidence for his claim.

An intelligence memo circulated to some in government in the weeks before the attack noted that one member of the terrorist group, since named as a perpetrator, had started to update his social media accounts with extremist content after the New Zealand shootings.

But terrorism researchers have said the sophisticated nature of the attack and the equipment used would probably have required months of preparation, including target reconnaissance, recruiting of the suicide bombers and obtaining explosives.

Meanwhile, footage of a suspected suicide bomber entering St Sebastian’s church in Negombo moments before the attack has emerged. The subsequent explosion, not shown in the video, was the deadliest of the series of coordinated bombings in Sri Lanka on Easter Sunday, with at least 110 people thought to have been killed. The footage was broadcast widely on Sri Lankan news channels.

One emerging scenario among western and south Asian security officials who spoke to the Guardian on Monday �“ before the Isis claim �“ was that the global group had established a connection with existing Sri Lankan networks of extremists already attracted by its ideology, but who lacked organisation and experience.

Sri Lankan veterans who had fought for Isis in Syria or Iraq may have acted as “connectors”, one South Asian official said, pointing to the group’s operations in Bangladesh in recent years as an example of how it had learned to “subcontract” to local militants.

The Isis claim was issued used terms familiar from previous such statements, citing “security sources” and describing the attackers as “fighters” of the group.

Until Isis began to lose its most important bases in the Middle East, the group’s claims of responsibility were treated as reliable indicators that it had been directly involved in an attack. In recent years, however, an increasing number of claims have been made for operations that either had nothing to do with the organisation or were only tenuously linked to it.

Wijewardene also told parliament on Tuesday that the death toll had climbed to 321 people �“ including 38 foreigners �“ and reiterated that the prime minister and other key officials were never told about the possibility of an impending attack.

(Source: The Guardian)