The American Foreign Service Association, the union that represents members of the U.S. Foreign Service, confirms diplomats in Havana were diagnosed with mild traumatic brain injury and hearing loss, along with symptoms including "cognitive disruption, and brain swelling."

AFSA says it met and spoke with 10 members of the Foreign Service who experienced damage to their health as a result of the attacks.

The State Department says at least 16 Americans have been affected by the "incidents" that began in late November 2016. Sources say five Canadians were also injured.

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Some were medically evacuated to Miami for treatment and testing, and a number opted to cut short their assignments in Havana. Intelligence analysts are focusing on whether infra- and ultrasonic waves from covert devices aimed at the homes of the diplomats, rented from the Cuban government, may have caused the injuries.

While the State Department hasn't announced a definitive cause or source of the attacks, it expelled two Cuban embassy officials in May. A source identifies them as Frank Silva Hernandez and Joel Lago Oliva, describing them as intelligence officials.

Cuba denies any involvement in the attacks.

Meanwhile, Russia has responded to suggestions it may have been involved, trying to drive a wedge between the U.S. and Cuba, following improving relations between the two countries under former President Barack Obama, who moved to restore full diplomatic ties.

Russian Foreign Ministry Spokesperson Maria Zakharova called the insinuations "absurd" at a press briefing in Moscow Thursday, and said "this does not help the normalization of the bilateral relations" between the U.S. and Russia.

"We are ready to help the Cuban side investigate the matter and determine the facts," she said.

The State Department refused to publicly comment on whether it would welcome Russia's involvement in the investigation into the attacks.

Steve Dorsey is a CBS News correspondent and CBS News Radio executive editor.