Several American diplomats who had been stationed in Cuba were forced to cut their tours of duty short and return home last year after suddenly and inexplicably losing their hearing.

According to a report by the Associated Press on Wednesday, unnamed US officials conducted an investigation into the incidents and found that an “advanced sonic weapon” was responsible. The sonic devices were planted in or around the diplomats’ homes and emitted inaudible sounds that apparently caused the hearing loss.

The day after the original report was published by the Associated Press, the Canadian government told the news agency that one of its diplomats in Cuba had also been treated for hearing loss.

Officials in Canada “are aware of unusual symptoms affecting Canadian and US diplomatic personnel and their families in Havana,” a spokesperson for Global Affairs Canada told the AP. “The government is actively working—including with US and Cuban authorities—to ascertain the cause.”

The US State Department confirmed that diplomats had “a variety of physical symptoms” and said the US responded by removing two Cuban diplomats from the country’s embassy in Washington last May.

The Cuban government denied the allegations, and said the expulsion of the Cuban diplomats was “unjustified and baseless.”