A little-known Islamist group formerly known for vandalising Buddhist statues, National Thowheeth Jama’at, has been named the prime suspect in Sunday's attacks.
But Sri Lanka's presidency added that "intelligence sections have reported that there are international terror groups which are behind local terrorists."
Sri Lanka's religious make up
Less than eight per cent of Sri Lanka's population of 21 million are Christian, with many of the population Roman Catholic; Hindus amount to 12.6 per cent and Muslims nearly 10 per cent.
The vast majority are Buddhist, according to the country’s 2012 census.
Sri Lanka's Christians are mainly of Portuguese descent, and to some extent Dutch colonists.
But despite the small percentage of Christians, "97 incidents" of attacks on churches, intimidation and violence have been recorded by the National Christian Evangelical Alliance of Sri Lanka since 2017.
Rucki Fernando, a human rights activist, said there have been regular cases of "local villagers or Buddhist monks intimidating a pastor or interrupting a prayer service."
"Sri Lankan governments have overlooked violence against religious minorities - both Christians and Muslims -- that has been on the rise in recent years," he said.
"But we have never seen anything of this scale or magnitude before."
Early last year there were a series of religious clashes between Sinhalese Buddhists and Muslims in the central district of Kandy.
Three people were killed and hundreds of homes destroyed.
At the time, the government temporarily shut down social media sites Facebook and WhatsApp to try and halt anti-Muslim violence.
Some social media sites were also blocked after Sunday's attacks.
How do the Easter Sunday attacks differ from the civil war?
Mr Kingsbury said the Sri Lankan civil war, which ended in 2009, was based around nationalism and ethnic identity rather than religion.
But, he said, these attacks were different.
“It would appear very much that Christians have been the primary target of these bombings, although the wider campaign would appear to be attacking westerners,” Professor Kingsbury said.
Mr Kingsbury said it’s still unclear what the group behind the attacks' primary motivation was.
“What is known is that a number of Muslim Sri-Lankans did travel to the Middle East in recent times and joined with Al-Quaeda and/or Islamic State; some of those fighters have now returned to Sri Lanka,” he said.
“The high level of organisation of the bombings seems to indicate that at least some of them are amongst those who have returned from fighting in the Middle East.
“If that’s correct, the targeting of Christians would appear to be part of a wider global jihadi agenda, not a specifically Sri Lankan agenda.”
Australian National University terrorism expert Clive Williams said the attacks fit a general narrative "among Muslims, that they have been victimised by crusaders and Christians over many centuries."
“They think that Christians are responsible for discrimination and atrocities against Muslims and they will go back to the periods of the crusades and what was done to Muslims during the crusade," he said.
According to Mr Kingsbury, because Christians are a minority in Sri Lanka they are particularly vulnerable.
“In all this, there’s a notion that we are the pure community, that means outsiders, or the other, are impure and must be excluded, removed, got rid of. It’s a global trend towards nationalism or religious chauvinism,” he said.
Cardinal Malcolm Ranjith, archbishop of Colombo, said those behind the attacks should be punished "mercilessly".
"Only animals can behave like that," he said.