The State Department says it is investigating another "incident" in June that injured U.S. diplomats in Cuba.

The unspecified incident is now part of the ongoing investigation into the matter, according to State Department spokesperson Heather Nauert. The State Department also increased the confirmed number of affected U.S. personnel to 19, up from the 16 previously reported. The latest assessments of the attacks suggest inaudible sound -- ultra- and infrasonic waves -- are responsible.

In August, CBS News obtained exclusive medical records showing American diplomats were diagnosed with conditions as serious as mild traumatic brain injury, and likely damage to the central nervous system. The State Department said the incidents began in late November 2016. A source familiar with the incidents told CBS News officials are investigating whether the diplomats were targets of a sonic attack at their homes, which are provided by the Cuban government.

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"We continue to ensure our personnel receive the best possible medical evaluation and care," Nauert said. "Embassy Havana has a medical officer on staff, and we have had consistent medical coverage at post through the reported incidents. We can't rule out new cases as medical professional continue to evaluate members of the embassy community."

The American Foreign Service Association, which represents members of the U.S. Foreign Service, confirmed to CBS News that members of the service were diagnosed with mild traumatic brain injury and hearing loss, as well as symptoms like "cognitive disruption, and brain swelling." The AFSA said it met with 10 members of the Foreign Service who experienced damage to their health.

Five Canadian diplomats in Cuba were also injured.

Cuba denies any role in the attacks.

Russian Foreign Ministry Spokesperson Maria Zakharova has called insinuations that Russia is responsible "absurd."

CBS News' Steve Dorsey contributed to this report.