Sri Lanka’s state minister of defence has said the Easter attack on churches, hotels and other sites in the South Asian nation was “carried out in retaliation” for the shooting massacre at two New Zealand mosques last month, according to a statement.

The minister, Ruwan Wijewardene, told Parliament the government possessed information that the series of bombings in and outside of Colombo that killed more than 300 people were carried out “by an Islamic fundamentalist group” in response to the Christchurch attacks.

He did not provide evidence of explain the source of the information.

Mr Wijewardene blamed “weakness” within Sri Lanka’s security apparatus for failing to prevent the nine bombings at churches, luxury hotels and other sites.

“By now it has been established that the intelligence units were aware of this attack and a group of responsible people were informed about the impending attack,” he said.

Sri Lanka Church Blasts
Investigators at the scene of a suicide bombing at St Sebastian Church in Negombo (Gemunu Amarasinghe/AP)

“However, this information has been circulated among only a few officials.”

As Sri Lanka’s leaders wrangled the aftermath of an apparent homegrown militant attack and massive intelligence failure, security was heightened on Tuesday for a national day of mourning and the military was employing powers to make arrests it last used when the devastating civil war ended in 2009.

The six near-simultaneous attacks on three churches and three luxury hotels and three related blasts later Sunday were the South Asian island nation’s deadliest violence in a decade.

Mr Wijewardene said the death toll from the attack now stood at 321 people, with 500 wounded.

Word from international intelligence agencies that a local group was planning attacks apparently did not reach the prime minister’s office until after the massacre, exposing the continuing political turmoil in the highest levels of the Sri Lankan government.

On April 11, Priyalal Disanayaka, Sri Lanka’s deputy inspector general of police, signed a letter addressed to the directors of four Sri Lankan security agencies, warning them that a local group was planning a suicide attack in the country.

Sri Lanka Church Blasts
An investigator at the scene of a suicide bombing (Gemunu Amarasinghe/AP)

The intelligence report attached to his letter, which has circulated widely on social media, named the group allegedly plotting the attack, National Towheed Jamaar, said it was led by Zahran Hashmi, and was targeting “some important churches” in a suicide terrorist attack that was planned to take place “shortly”.

The report named six individuals likely to be involved in the plot.

On Monday, Sri Lanka’s health minister held up a copy of the intelligence report while describing its contents, spurring questions about what Sri Lanka police had done to protect the public from an attack.

Among the 40 people arrested on suspicion of links to the bombings were the driver of a van allegedly used by the suicide bombers and the owner of a house where some of them lived.

Heightened security was evident an international airport outside the capital where security personnel walked explosive-sniffing dogs and checked car boots and questioned drivers on roads nearby.

Police also ordered that anyone leaving a parked car unattended on the street must put a note with their phone number on the windscreen, and post officers were not accepting pre-wrapped parcels.

A block on most social media since the attacks has left a vacuum of information, fuelling confusion and giving little reassurance the danger had passed.

Even after an overnight curfew was lifted, the streets of central Colombo were mostly deserted Tuesday and shops closed as armed soldiers stood guard.

Sri Lankan authorities also Tuesday planned to brief foreign diplomats and receive assistance from the FBI and other foreign intelligence-gathering agencies.

The country’s prime minister Ranil Wickremesinghe said he feared the massacre could unleash instability and he vowed to “vest all necessary powers with the defence forces” to act against those responsible.

Authorities said they knew where the group trained and had safe houses, but did not identify any of the seven suicide bombers, whose bodies were recovered, or the other suspects taken into custody.

All seven bombers were Sri Lankans, but authorities said they strongly suspected foreign links.

Also unclear was a motive.

Sri Lanka Church Blasts
Catholic nuns attend a funeral service in Sri Lanka (Gemunu Amarasinghe/AP)

The history of Buddhist-majority Sri Lanka, a country of 21 million including large Hindu, Muslim and Christian minorities, is rife with ethnic and sectarian conflict.

In the 26-year civil war, the Tamil Tigers, a powerful rebel army known for using suicide bombers, was finally crushed by the government in 2009 but had little history of targeting Christians.

Anti-Muslim bigotry fed by Buddhist nationalists has swept the country recently, but there is no history of Islamic militancy.

Its small Christian community has seen only scattered incidents of harassment.

The office of New Zealand’s prime minister said she was aware of the comments linking Sri Lanka’s Easter bombings to the mosque attacks in Christchurch, though it has not “seen any intelligence upon which such an assessment might be based”.

Jacinda Ardern’s office also added that it understood “the Sri Lankan investigation into the attack is in its early stages”.