The country's authorities are monitoring Islamic State recruits who have returned to the country, PM Ranil Wickremesinghe said on Tuesday.
"The security officials who got the intelligence report from a foreign nation did not share it with me".
"A broader goal of this shadowy group may be to instill terror - just like al-Qaida and ISIS - the groups that NJT appears to model itself on", Kugelman told VOA.
"We will be following up on IS claims, we believe there may be links", Wickremasinghe stated.
The Sri Lankan government has blamed the bombings on a little-known domestic Muslim militant group called National Thowfeek Jamaath.
Government spokesman Rajitha Senaratne said the warning was not passed on to Wickremesinghe or other top ministers.
New Zealand's Prime Minister Jacinda Ardern said on Wednesday that her government was not aware of any intelligence suggesting that a devastating attack on Easter Sunday in Sri Lanka was in retaliation for deadly shootings on a mosques in Christchurch.
The jihadist group claimed responsibility for the attacks earlier on Tuesday, some 48 hours after the near-simultaneous blasts tore through three high-end hotels popular with foreigners and three churches packed with Christians marking Easter.
Who could be behind the attacks?
IS said it had "targeted nationals of the crusader alliance [anti-IS US-led coalition] and Christians in Sri Lanka" via its Amaq news outlet.
The group's last territory fell in March but even then experts had warned it does not mean the end of IS or its ideology. He gave no further details.
"This man had also checked into the hotel the previous day", an official source told Agence France-Presse of the terrorist.
During anti-Muslim riots in Sri Lanka previous year, the NTJ used social media to highlight discrimination against Muslims in the country, such as setting up Buddhist symbols in the northeast where no Buddhists lived.
Kugelman said the group's main activities in the past months have consisted of targeting Buddhist statues as the country's Buddhists feuded with Muslims.
Explosions occurred in eight different locations in Sri Lanka.
Three churches and four hotels were hit by suicide bombers on Sunday morning, killing 321 people and wounding 500, sending shockwaves through an island state that has been relatively peaceful since a civil war ended a decade ago.
Sri Lankan officials said 38 foreign nationals were among the dead, with another 14 unaccounted for.
The death toll from the Easter Sunday bomb attacks in Sri Lanka has risen beyond 320.
A mourner places flowers on a grave during a funeral of Easter Sunday suicide bomb blast victim at Methodist cemetery in Negombo, Sri Lanka.