Some of the diplomats hurt in a mystery "sonic harassment attack" on the U.S. embassy in Cuba suffered brain injuries or permanent hearing loss, their staff association said Friday.

Washington recently said at least 19 embassy employees were injured in a series of incidents in Havana that began last year, but officials have not revealed the extent of the injuries.

Now, the American Foreign Service Association -- the labor union representing U.S. diplomatic and international aid personnel -- has been able to speak to 10 of those who received treatment

"Diagnoses include mild traumatic brain injury and permanent hearing loss, with such additional symptoms as loss of balance, severe headaches, cognitive disruption and brain swelling," it said.

What transpired in Havana in late 2016 and early 2017 has remained an elusive mystery as U.S. investigators continue looking for a device or other possible cause for what the State Department has described as attacks on diplomats' health.

Early indications from U.S. officials had pointed to a possible covert sonic device, although investigators have not said such a device has been found. The State Department has said it still can't conclude who was responsible for the attacks.

The confirmation that diplomats suffered traumatic brain injury suggested the attacks caused more serious damage than the hearing-related complaints that were initially reported.

Traumatic brain injury, or TBI, typically results from a bump, jolt or other external force that disrupts normal brain functioning, according to the U.S. Centers for Disease Control and Prevention. Short- and long-term effects can include changes to memory and reasoning, sight and balance, language abilities and emotions.

Not all traumatic brain injuries are the same. Doctors evaluate patients using various clinical metrics such as the Glasgow Coma Scale, in which a numerical score is used to classify TBIs as mild, moderate or severe.