State Department spokesperson Heather Nauert said Wednesday that officials first learned about the "incidents" at the usa embassy in Cuba in late 2016.
The information comes a day after the US government said it believed some of its diplomats in Havana had been targeted with a covert sonic device that left them with severe hearing loss.
In fact, American diplomats who were stationed in Cuba in 2016 returned home with hearing-loss issues.
It said the decision to expel two Cuban diplomats from Washington had been "unjustified and unsubstantiated". "The AP says Cuba may have placed sonic devices that produce non-audible sound inside or outside the residences of several embassy staffers with the intent of deafening them", he reported. "We're taking this incident very seriously, and it's under investigation right now".
Nauert confirmed that two Cuban diplomats were asked to leave on May 23rd and they've since departed.
A series of "bizarre" incidents attributed to a "covert sonic device" led to several U.S diplomats experiencing unexplained hearing losses, The Associated Press reported.
Nauert did not provide further details about the cause or consequences of the symptoms, other than to say that they were not life-threatening.
The U.S. officials weren't authorized to discuss the investigation publicly and spoke on condition of anonymity.
The U.S. diplomatic mission in Havana was only elevated to status of embassy in 2015, when then-President Obama and Cuban President Raul Castro reestablished full relations after half a century of Cold War hostilities. "It's virtually impossible for anyone to take action against an American diplomat without an element of the Cuban state being aware".
"We requested their departure as a reciprocal measure since some USA personnel's assignments in Havana had to be curtailed due to these incidents", Nauert said.
"We don't know exactly what...what this requires is providing medical examinations to these people", Nauert said.
Speaking to CNN, a USA official added: "We felt like we needed to respond to the Cubans and remind them of their responsibility under the Vienna convention".
The FBI and the Diplomatic Security Service are investigating and, speaking on condition of anonymity, a United States government official told CNN that some staff had suffered permanent hearing loss.
The Cuban foreign ministry responded to the allegations saying it was also investigating the situation.