Diplomats in Havana have reportedly struggled with memory, balance and vision after a strange series of unexplainable symptoms that the U.S. has deemed “health attacks.”

At least one Canadian diplomat and 16 U.S. government employees in Cuba have reported symptoms of hearing loss since late last year.

According to a report from CBS News, some of those patients have since been diagnosed with mild brain trauma and damage to the central nervous system.

In the most severe cases, some diplomats were reportedly forced to cut their tours short and return home.

Global Affairs has said it was aware of “unusual symptoms” that affected at least one Canadian diplomat abroad, but the exact number of Canadians hospitalized is unclear. The agency says there is no reason to believe that any Canadians vacationing in Cuba were affected.

Global Affairs has said it is actively working with U.S. and Cuban authorities to uncover the cause.

U.S. officials have said they suspect a sonic weapon operating at a register undetectable to the human ear may be to blame.

Sonic weapons aren’t unheard of. Devices such as the long-range acoustic device, or L-RAD, have been used to disperse crowds with a loud boom.

However, Canadian audiologist Robert Harrison says he has doubts about the theory since most diplomats reported not hearing anything.

“I find it implausible that any sonic device which is not heard by the victim can have any effect on the hearing, on the auditory system or on the brain,” Harrison told CTV News.

The lack of certainty hasn’t stopped the U.S. from taking action. In May, two Cuban diplomats were expelled from the country, and U.S. Secretary of State Rex Tillerson has pointed the finger squarely at Cuban officials to sort out what happened.

"We hold the Cuban authorities responsible for finding out who is carrying out these health attacks on not just our diplomats but, as you've seen now, there are other cases with other diplomats involved," Tillerson said on Aug. 11.

Cuba has denied any involvement in a suspected sonic attack.

With a report from CTV’s Kevin Gallagher and the Associated Press