Dhaka: An eight-year-old relative of Bangladeshi Prime Minister Sheikh Hasina was among 321 people killed in the Easter Sunday suicide bombings in Sri Lanka.

Zayan Chowdhury, who was also a relative of British Labour MP Tulip Siddiq, was having breakfast with his father at a hotel in Colombo when a suicide bomber detonated his device. The boy's mother and younger brother were in their hotel room at the time, bdnews24.com reported.

Chowdhury was the grandson of Sheikh Fazlul Karim Selim, a leader of Bangladesh's ruling Awami League party and cousin of Hasina.

The Dhaka Tribune reported that the boy's father was injured in the blast and admitted to a hospital.

Meanwhile, the United Nations on Tuesday said that 45 children were killed in the Sri Lanka bloodbath.

"The total now is 45 children who died," UNICEF spokesman Christophe Boulierac told reporters in Geneva, stressing that others children "are wounded and are now fighting for their lives", meaning the toll among minors from the Sunday attacks could rise.

The Islamic State terror group claimed responsibility for the carnage which also injured 500 people.