A post shared on Twitter on Tuesday read: “Security Source to Amaq agency: Those who carried out the attack that targeted the citizens of the coalition and Christians in Sri Lanka the day before yesterday were from the fighters of the Islamic State.”
The group did not give evidence for its claim.
The bombings were a retaliation for the recent deadly attacks on mosques in New Zealand, a Sri Lankan official said.
The toll rose to 321 dead on Tuesday with about 500 people wounded.
“The initial investigation has revealed that this was in retaliation for the New Zealand mosque attack,” junior minister for defence Ruwan Wijewardene told parliament.
He did not elaborate on why authorities believed there was a link to the killing of 50 people at two mosques in the New Zealand city of Christchurch during Friday prayers on March 15. A lone gunman carried out those attacks.
Wijewardene said two Sri Lankan Islamist groups - the National Thawheed Jama’ut and Jammiyathul Millathu Ibrahim - were responsible for the blasts early on Sunday during Easter services and as high-end hotels served breakfast.