Security personnel inspect the interior of St. Sebastian's Church in Negombo on April 22, 2019, a day after the church was hit in series of bomb blasts targeting churches and luxury hotels in Sri Lanka.

A fifth-grade student at an exclusive private school in Washington, D.C., and a Denver man on a business trip were among the U.S. residents killed in the Sri Lanka Easter attacks, a media report and the man's employer said on Monday.

Suspected suicide bombers set off explosions in at least seven churches and hotels in the capital Colombo on Easter Sunday, killing 290 people and wounding nearly 500.

U.S. Secretary of State Mike Pompeo said "several" Americans were killed without providing a precise number.

Kieran Shafritz de Zoysa, a fifth-grader at Sidwell Friends, died in one of the blasts, the school emailed to friends and family, according to CNN. Fifth-graders are around 10 years old. Staff at the school did not respond to requests for confirmation.

"Passionate about learning, he adored his friends, and was incredibly excited about returning to Sidwell Friends in the coming school year," school principal Mamadou Gueye wrote in the email, CNN reported.

The boy's citizenship was unknown.

Sidwell Friends is the school where President Barack Obama's daughters Sasha and Malia and President Bill Clinton's daughter Chelsea attended.

Dieter Kowalski, a Wisconsin native who lived in Denver, was also among the victims. He was on a business trip for the British education publishing company Pearson, which has 800 employees in Sri Lanka.

"Dieter had just arrived at his hotel, where many of our colleagues have stayed over the years, when he was killed in an explosion," Pearson CEO John Fallon said on LinkedIn.

All other Pearson employees in Sri Lanka have been accounted for, Scott Overland, a Pearson spokesman, wrote in an email.

A senior leader on a technical services team, Kowalksi was on assignment to work with local Pearson engineering teams, Fallon said."Colleagues who knew Dieter well talk about how much fun he was to be around, how big-hearted and full-spirited he was. They tell of a man to whom we could give our ugliest and most challenging of engineering problems, knowing full well that he would jump straight in and help us figure it out," Fallon said.

Kowalski himself appeared enthusiastic about his trip, posting a map on Facebook showing the path from Denver to Colombo.

"And the fun begins. Love these work trips. 24 hours of flying. See you soon Sri Lanka!" Kowalski said in his final Facebook post on Friday.

The comments section became a forum for condolences from more than 200 people.