U.S. and Canadian diplomats in Cuba suffered mild traumatic brain injury and likely damage to their central nervous system in an incident that has been linked to a sonic attack.

Medical records said doctors had discovered signs of the damage after patients complained about hearing loss, nausea, headaches and balance problems, CBS News reported.

More than 10 U.S. and 5 Canadian diplomats in Havana began experiencing "a variety of physical symptoms" in the fall of 2016, according to the State Department.

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The symptoms have been traced to a sonic attack — a deliberate use of a sonic device operating outside of the audible range — on diplomatic residences in Havana.

Cuban authorities have vowed to investigate the injuries amid pressure from Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE.

Some diplomatic tours of duty have also been cut short as a result of the incident.

The attacks come as U.S.-Cuba relations have soured under President Trump, following a period of rapprochement under his predecessor, Barack Obama Barack Hussein ObamaTwitter investigating automated image previews over apparent algorithmic bias Donald Trump delivers promise for less interventions in foreign policy Rush Limbaugh encourages Senate to skip hearings for Trump's SCOTUS nominee MORE.

Although the State Department has not officially blamed the Cuban government, the U.S. expelled two Cuban diplomats in May in connection to the attacks, The Washington Post reported.