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.

Officials are investigating whether the diplomats were targets of some form of sonic attack directed at their homes.

Incidents had continued to occur on the island and some US diplomats had cut short their assignments.

The state department did not immediately respond to requests for a comment on the CBS News report.

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.

Heather Nauert, state department spokeswoman, said two weeks ago the state department learned of incidents at its embassy in Havana in late 2016. She said the source or cause of the "incidents" was unknown but they "caused a variety of physical symptoms" in US government employees.

Several US citizens at the embassy were evacuated to the United States over the past six months for treatment of a variety of complaints. Some subsequently received hearing aids.