The United States said it had expelled two Washington-based Cuban diplomats in May after unspecified "incidents" caused physical symptoms in Americans serving at the U.S. Embassy in Havana that an unnamed official said included hearing loss.
She said: "We don't have any definitive answers about the source or the cause of what we consider to be incidents".
"The safety and security of American citizens at home and overseas is our top priority", Nauert said while she emphasized the Cuban government is obligated under the Geneva Convention to protect US diplomats.
One State Department official confirms reports that these "incidents" involved symptoms of hearing loss.
They had been reporting physical symptoms resembling concussions since the latter half of 2016 but it is believed that those affected were not at the same place at the same time. The AP also reports an investigation concluded that an advanced sonic weapon placed in or around the diplomats' homes was to blame.
According to The Associated Press, the affected Americans were complaining of hearing loss.
The US embassy in Havana only opened in 2015 as part of former President Obama's rapprochement with Cuba.
Nauert confirmed that two Cuban diplomats were asked to leave on May 23rd and they've since departed.
The ministry said it had created an expert committee to analyze the incidents and had reinforced security around the USA embassy and US diplomatic residences.
"We requested their departure as a reciprocal measure since some United States personnel's assignments in Havana had to be curtailed due to these incidents", she said.
In a statement, the Cuban foreign affairs ministry said it launched an investigation after it was informed of the situation by United States officials in February. Officials cautioned the AP that Cuba may have been unaware the attacks were happening, and that a third country like Russian Federation may have been responsible.
Cuba responded by saying that it would never allow its soil to be used for actions against diplomats and that it is willing to cooperate with the U.S.to clarify the incidents.
Ms Nauert said the government was taking it "very seriously, and there is an investigation now under way".
"This has not stopped with President Obama's appeasement". Some had to go to the USA for treatment and one is thought to have become permanently deaf.
The Cuban authorities set up an inter-institutional expert committee for the analysis of the facts; expanded and reinforced the protection and security measures of the mission, its staff and diplomatic residences; and new channels were made available for direct communication between the Embassy and the Department of Diplomatic Security.