Three students at Ballou Senior High School in Southeast Washington became ill Monday morning after they reported eating apples provided by a teacher, according to the D.C. Fire Department.

But city officials said the cause of the ailments remains under investigation, and that “apples have not been identified as the source of the illness.”

The incident drew dozens of firefighters and paramedics to the school in the 3400 block of Fourth St. SE in Congress Heights.

Battalion Chief Brian Lee, a fire department spokesman, said the three students were taken by ambulance to Children’s National Medical Center complaining of stomach aches. He said as many as seven other students were evaluated on a Fire Department bus dispatched to the high school.

The interim director of the D.C. Department of Health, Dr. Saul Levin, said in a statement that a “cluster of several students” reported falling ill “after consuming apples brought in by a teacher.” He said three students were treated for nausea and other gastroenteritis symptoms.

Levin’s statement said that epidemiologists are trying to investigate the source of the illness and that a food safety team inspected the school’s kitchen, but found nothing wrong.

This post has been updated.