Reports that the Sri Lankan suicide bombings over Easter weekend were retaliation for the Christchurch mosques terror attacks and were carried out by IS are being treated with caution by the New Zealand and Sri Lankan governments.
Sri Lankan junior defence minister Ruwan Wijewardene has said the initial evidence shows the terror attacks on three churches and four hotels across the country, which have now killed 321 people including 45 children, were in retaliation for last month's mosque shootings in Christchurch, New Zealand.
Some observers doubt the Sri Lankan horror could have been concocted in the six weeks since the 15 March mosque attacks in Christchurch, so could not have been provoked by them.
IS has also claimed responsibility for the eight suicide bombings, claiming through its news agency it has learnt the bombers were Islamic State fighters. In the past, IS has sometimes claimed attacks that it was not involved in or which it simply inspired, but the choice of targets is much more in line with IS ideology than with the traditional types of communal violence seen in Sri Lanka.
The organisation also made no mention of the Christchurch attacks, and provided no proof of the bombers' affiliations.
New Zealand's Prime Minister Jacinda Ardern has expressed caution about the claims.
"We've seen nothing officially and we've received no intelligence to confirm that," she told Morning Report.
She said she would not get into a debate about whether the Sri Lankan minister should have made the claims about retaliation, and Sri Lanka needed to be allowed to focus on their response.
Her Sri Lankan counterpart Ranil Wickremesinghe has also said it was too early in the investigation to link the attacks.
"It's possible it could have been because of the Christchurch attacks, we cannot say yet. I think the police, once they question ... will be able to find out."
The Sri Lanka government has maintained that the attacks on Sunday could not have been carried out without support from terror groups abroad.
Sri Lanka's government has blamed the blasts on local Islamist group National Thowheed Jama'ut, a claim backed by the defence minister who claimed there was a link to the New Zealand attacks.
"It was done by National Thawheed Jama'ut along with JMI," Mr Wijewardene said, referring to another local group, Jammiyathul Millathu Ibrahim.
NTJ has no history of large-scale attacks but came to prominence last year when it was blamed for damaging Buddhist statues. The group has not said it carried out Sunday's bombings.
Sunday's attacks have highlighted rifts in Sri Lanka's leadership, after it emerged that authorities were warned about an imminent threat from the NTJ jihadist group. Mr Wickremesinghe and the cabinet were not informed, ministers said.
Mr Wickremesinghe also said the 40 suspects arrested so far were all Sri Lankan citizens, however some were thought to have travelled overseas. There have been suggestions that a Syrian national was among the attackers, pointing to the possibility they were associated with IS.
"There seems to have been foreign involvement, they feel that some of them [the terrorists] might have travelled abroad and come back. There may be more than that, that's what we want to find and that's why we have asked for assistance on this issue."
''We ... are of the view there are foreign links and some of the evidence points to that. So if the IS (Islamic State) claimed it, we will be following up on this claim," he said.
Attacks "very unlikely" retaliation - security expert
Security expert Paul Buchanan said he thought the two attacks were "very unlikely" to be linked.
"I would take these claims with a very healthy dose of scepticism, and the reason for that is both ISIS and the Sri Lankan government have their own reasons to deflect from the local nature of the attack. ISIS of course is on the run and wants to claim things that are possibly beyond its scope at this point but make the event broader than it is and the Sri Lanka government wants to deflect from its failures of intelligence that facilitated this.
"More importantly, the amount of preparation and planning needed to undertake these coordinated simultaneous attacks simply is too long for it to have been attributed to the March 15 attacks. We're a month out from the March 15 attacks, they were getting intelligence warnings ... that people were stockpiling explosives before March 15th."
Falling into retaliatory rhetoric over the attacks is dangerous, he said.
"We fall into the false narrative of the clash of civilisations," he said.
"If we get into tit for tat attacks ... we get into a cycle of violence that quite frankly has not occurred in the past. In the past, attacks are done randomly.
"The way the global media is covering it is falling into that trap and conservative media outlets around the world have already cast this as a 'Christianity versus Islam' thing when in fact ... both Muslims and Christians are a distinct minority in Sri Lanka and they're both oppressed by Buddhists.
"If I look at the methodology of the attack I think 'well, the Catholic churches were attacked because they were incredibly soft targets and they were not defended ... even in spite of the intelligence warnings to the government about the choice of targets.
"The attacks on the hotels are clearly designed to hurt tourism business in Sri Lanka, on which it depends very very strongly."
Researcher suggests link between attacks possible, likely with backing from major group
A terrorism researcher at the London-based Asia-Pacific Foundation, Sajjan Gohel, said a connection between the two attacks was possible.
"This attack didn't happen overnight, we're talking about a lot of planning reconnaissance, because the attack was so well coordinated and synchronised."
"We do know that after the Christchurch attack, ISIS specifically called for attacks during the Easter holidays. Could this have been put together in that time? Not necessarily, but perhaps the timing coincided then with a motivation to bring the plot forward."
He said the scale of the attack showed it was likely backed by a powerful transnational actor.
"This was a huge terrorist attack because of how well coordinated it was: in multiple locations, near simultaneous explosions, well researched by the terrorists in terms of the targets - the churches, the luxury hotels.
"[The] local outfit that the authorities have named are pretty much an ordinary violent gang - they have been involved in defacing statues, doing graffiti on walls, nothing on this scale.
"We're talking about a major leap if they've moved from petty organised criminal activity to carrying out one of the biggest attacks that we've seen - bigger than the Bali bombings, the Madrid train bombings."
Victoria University of Wellington social and cultural studies lecturer Rick Weiss told Morning Report his concern was more about the Sri Lankan communities.
"Muslim and Christian communities in Sri Lanka have tended to get along in the past and in fact both have been targeted by Buddhist nationalist groups. In many ways they've been together on the wrong side of being a minority religious community."
He said the type of attack probably pointed to a more international component, and it was important for the government and leaders of religious groups to stand together against the violence.
"I think they need to react in very strong ways, affirming solidarity in many of the ways we saw the New Zealand government react to the Christchurch shootings.
"The communities involved also have to reject that violence quite strongly. These attacks are always extremist groups, right, they're always representing a kind of minority division and so the mainstream voices for these different religious communities have to come out and assert their solidarity."