5th-grader from prestigious Washington D.C. school among victims of Sri Lanka bombings

A fifth-grade student at a prestigious Washington D.C. school was among the victims of a series of deadly bombings that shook Sri Lanka on Easter Sunday, killing at least 290 people and injuring 500 others.

Kieran Shafritz de Zoysa died when a wave of near-simultaneous explosions rocked three churches and three luxury hotels on the island nation, the Sidwell Friends School said in a letter sent to students and parents.

Kieran was expected to return to the school after a leave of absence to study and live in Sri Lanka, the school said.

"Kieran was passionate about learning, he adored his friends, and he was incredibly excited about returning to Sidwell Friends this coming school year," the school said in a letter. "We are beyond sorry not to get the opportunity to welcome Kieran to the Middle School."

Sidwell Friends School serves students from pre-kindergarten to 12th grade and has been home to notable alumni including Chelsea Clinton and Malia and Sasha Obama.

The school asked parents to discourage their children from discussing the boy's death in group messaging services and said that counselors would be made available.

The Sunday bombings occurred during church services and Easter brunch at the hotels. The blasts collapsed ceilings and blew out windows.

The attacks were carried out by seven suicide bombers, and 24 suspects have been arrested, authorities said Monday. Police later reported two additional explosions.

The six almost-simultaneous blasts took place at the Cinnamon Grand, Shangri-La and Kingsbury hotels in Colombo, as well as three churches.

Dieter Kowalski, 40, a Denver man on a work trip staying at the Cinnamon Grand was one of four Americans who died in the explosions.

Kowalski worked for Pearson, an education publishing and assessment firm, who confirmed his death in a statement.

"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 wrote in a note to employees.

Colleagues described Kowalski as big-hearted, full-spirited and fun to be around, Fallon wrote.

The Department of State said that several U.S. citizens were also injured in the attacks.

Staff at a hospital in Colombo told NBC News that they treated an American woman identified as Chimai Tran-Luu, adding that she was later discharged.

Three children of Danish billionaire Anders Holch Povlsen, who owns the clothing company Bestseller and is a shareholder in online retailer ASOS, were also killed in the attack, a company spokesman confirmed to NBC News.

Government officials said Monday that Sri Lankan authorities had been warned about a potential terrorist plot just two weeks before Sunday's attacks. International intelligence agencies had informed Sri Lankan counterparts on April 4 that churches and tourist destinations were being targeted, according to the country's health minister.

Hemasiri Fernando, the chief of staff to Sri Lanka's president, also told NBC News that the country's security agencies had been alerted in advance.

According to Fernando, Sri Lankan officials were warned that "a small group" that was "very well organized and powerful" had been plotting an attack.

"We never expected it to be so big," Fernando said. "We never thought it would happen so soon."