In 2015, US and Cuban relations took a major turn, as America reopened the doors to its embassy in Havana.
One hypothesis, according to sources who spoke to the BBC, is that the hearing loss could have been caused by a sonic device whose emission of inaudible sound waves could cause deafness if placed outside the diplomats' homes. The report estimated that "about five" diplomats and spouses were affected and that American investigators had not yet concluded whether "the device was a weapon used in a deliberate attack, or had some other objective".
The U.S. officials weren't authorized to discuss the investigation publicly and spoke on condition of anonymity.
"Some United States government personnel who were working at our embassy in Havana, Cuba, on official duties have reported some incidents which have caused a variety of physical symptoms", State Department spokesperson Heather Nauert said.
Several State Department employees working in the building "were subjected to an "acoustic attack" using sonic devices that left at least two with such serious health problems they needed to be brought back to the U.S. for treatment", CNN reports.
"Cuba has never, nor would it ever, allow that the Cuban territory be used for any action against accredited diplomatic agents or their families", said the statement.
The Cuban Foreign Ministry got involved thereafter, and launched their own "exhaustive, high-priority, urgent investigation at the behest of the highest level of the Cuban government".
According to BBC, it is clear that the two Cuban diplomats left Washington in May.
It also led to the expulsion of the Cuban diplomats from the USA back in May. She did not describe the nature or cause of the symptoms, but said they started in 2016.
About five diplomats, including some spouses, had been affected, but no children were involved, United States officials said. Nauert would not go into detail about what had occurred, but Federal Bureau of Investigation and Diplomatic Security Service investigators were looking into the matter. But diplomats said that after the United States and Cuba restored full diplomatic ties in 2015, the campaign of harassment stopped.
It is thought that the devices were installed close to or inside the residences of diplomats, which are maintained by the Cuban government.
Investigators are exploring the possibility that another country, such as Russian Federation, carried out the attack without the Cuban government's knowledge.
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.
The statement from the Cuban Foreign Ministry said it had been informed of the incidents on February 17 and had launched an "exhaustive, high-priority, urgent investigation at the behest of the highest level of the Cuban government".