The University of Miami received a nervous call from the Trump administration: American diplomats in Havana were getting sick with headaches, dizziness and hearing loss. Washington needed answers.

At least six patients were flown from Cuba to the university’s hospital this year to determine the cause of a medical mystery that was dogging several people who worked at the American Embassy in Havana. The illnesses appeared to be caused by some kind of sonic wave machine, and the symptoms worsened with prolonged exposure, said a person who was briefed on the situation but was not authorized to comment.

One of the patients had a more serious illness that involved a blood disorder, the person said. This month, a University of Miami specialist went to Havana to examine others who work at the embassy, because officials expect that more people were affected.

On Friday, Secretary of State Rex W. Tillerson said the illnesses were a result of “health attacks,” adding, “We’ve not been able to determine who’s to blame.”