WASHINGTON (Reuters) – A doctor who evaluated American and Canadian diplomats working in Cuba diagnosed them with conditions as serious as mild traumatic brain injury and damage to the central nervous system, CBS News said on Wednesday, citing medical records it reviewed.

The diplomats had complained of symptoms including hearing loss, nausea, headaches and balance disorders after what were described as “incidents” that began affecting them in Havana beginning in late 2016, CBS News said.

Officials are investigating whether the diplomats were targets of some form of sonic attack directed at their homes, CBS reported, citing a source familiar with the incidents. The source said the incidents had continued to occur on the Communist-ruled island and that some U.S. diplomats had cut short their assignments there.

Asked about the CBS report, a U.S. State Department spokeswoman said the department did not have “definitive answers” on the source or cause of the incidents.

“An investigation into the incidents is ongoing,” the spokeswoman said.

The department said earlier this month that a number of Americans serving in Cuba had returned to the United States for “medical reasons” that were not life-threatening.

Spokeswoman Heather Nauert said two weeks ago the State Department learned of incidents at its embassy in Havana in late 2016. She said they “caused a variety of physical symptoms” in U.S. government employees.

Several U.S. citizens at the embassy were evacuated over the past six months for treatment of a variety of complaints. Some subsequently received hearing aids.

Although Washington expelled two Cuban diplomats over the incidents, Cuba has said it was investigating the U.S. allegations and would never allow its territory to be used for any action against diplomatic personnel or their families.

“The Cuban government has assured us it is also investigating and taking appropriate measures,” the State Department spokeswoman said on Wednesday.

A spokeswoman for Canada’s foreign ministry said Canada likewise was working to determine the cause.

“At this time, we do not have any reason to believe Canadian tourists and other visitors could be affected,” spokeswoman Brianne Maxwell told Reuters.