The State Department learned about the incident in late 2016, which the United States responded to by expelling two diplomats from the Cuban Embassy in Washington on May 23. The incidents left multiple employees with "a variety of physical symptoms", she said, and as a result the State Department "had to bring some Americans home".
Cuba's Ministry of Foreign Affairs issued a statement Wednesday night, saying it was informed of the alleged incidents by the U.S. Embassy in Havana and the U.S. Department of State on February 17. US officials told The Associated Press that about five diplomats, several with spouses, had been affected and that no children had been involved.
After months of investigation, U.S. officials concluded that the diplomats were exposed to an advanced device that operated outside the range of audible sound and was deployed either inside or outside their residences.
The Cuban government denied involvement in the incident, saying it would never allow actions against diplomats and their families.
The objection to removing the Cuban agents suggests that American officials did not merely want to reduce the number of staff in the embassy to balance the numbers following the departure of American officials from Havana. We're taking that situation seriously and it's under investigation right now.
Nauert told reporters that while the "incident" appears to have only affected State Department employees and not private USA citizens in Cuba, "we don't have any definitive answers about the source or the cause of what we consider to be incidents".
According to the news agency, a number of U.S. diplomats at the embassy in Havana began to experience hearing loss in the fall of 2016.
It comes a day after the U.S. said its diplomats in Havana were experiencing odd physical symptoms.
The FBI is now looking into the matter.
Given Trump's aggresive posture against the Cuban regime - and thorn of his comments about Castro's crimes - the fact that a more aggessive response from the U.S.to what amounts to an attack of USA diplomats in Cuba does not add up.
"We are aware of unusual symptoms affecting Canadian and United States diplomatic personnel and their families in Havana", a spokesperson for Global Affairs told the BBC.
Some subsequently got hearing aids, said the official, who spoke on condition of anonymity.
In response to the incidents, the United States expelled two Cuban diplomats from America in May.
About five diplomats, including some spouses, had been affected, but no children were involved, U.S. officials said.
It stressed that it had treated the issue "with utmost seriousness" and insisted that Cuba complies rigorously with the 1961 Vienna Convention, which applies special protections to diplomats.