A doctor who evaluated American and Canadian diplomats complaining about hearing loss and nausea while working in Cuba said they are suffering from traumatic brain injuries and possible damage to their central nervous systems, CBS reported on Wednesday.

Officials are investigating whether the diplomats were the targets of some type of sonic attack aimed at their homes, which were provided by the Cuban government, the network reported, citing a source.

The diplomats said they had symptoms that included hearing loss, nausea, headaches and balance disorders after the State Department said “incidents” began affecting them near the end of 2016, the report said.

Many of the diplomats were so stricken, they had to cancel their tours early and return home.

The University of Miami Health System confirmed in a statement to CBS that its doctors were “consulted” by the State Department about its diplomats in Cuba.

“Like any top-notch academic medical center in the nation, the University of Miami is often consulted regarding complex health care issues or emerging diseases. In the case of US diplomats, our physicians were consulted by the State Department,” read the statement from the university.

The State Department warned the Cuban government of its responsibility to protect diplomats and expelled two officials at the Cuban embassy in Washington on May 23 in retaliation.

Secretary of State Rex Tilleson said earlier this month that “we hold the Cuban authorities responsible for finding out who is carrying out these heath attacks.”

Cuba denies any involvement in the attacks.