She explained in a video that has been posted on YouTube that the department did not have definitive information on the source or cause of the incidents but could confirm that, on May 23, the State Department took further action and investigations are ongoing.
"The safety and security of USA citizens is our top priority", Nauert said, adding that "the Cuban government has a responsibility and obligation to protect our diplomats under the Geneva Convention".
State Department spokesperson Heather Nauert said Wednesday that officials first learned about the "incidents" at the U.S. embassy in Cuba in late 2016. She did not describe the nature or cause of the symptoms, but said they started in 2016.
"The Cuban government has been harassing United States personnel working in Havana for decades", he said.
State Department spokeswoman Heather Nauert would not provide details, except to say it had caused medical but non-life-threatening problems for an unspecified number of U.S. Embassy personnel based in Havana. The AP also reported that investigators are trying to determine if the Cuban government used sonic devices that create non-audible noise to try to deafen the Americans.
One official told the Associated Press news agency that it could be potentially permanent hearing loss.
According to reports, the diplomats were targeted with a sonic device that had been placed or planted where they lived.
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.
The government of Cuba has denied any wrongdoing after facing charges from Washington that US embassy staff in Havana fell ill with unspecified symptoms while working in the country, resulting in their departure from the Caribbean nation.
Meanwhile, on Fox News Channel's Special Report, Anchor Bret Baier delivered a news brief on the developing story.
The Cuban government, Nauert said, has a "responsibility and an obligation under the Geneva Convention to protect our diplomats". 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 has never, nor would ever, allow the Cuban territory to be used for any kind of action against accredited diplomats or their families", the ministry said.
Global Affairs Canada, the coutnry's foreign ministry, says the government is working with the USA and Cuban governments to find out what happened.
The foreign ministry said it had started a "comprehensive, priority and urgent investigation" into the alleged incidents after it had been informed of them by the USA embassy in February. "And we take this extremely seriously".
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.
Relations with the country have become a significant issue in U.S. politics, he explained, thanks in part to the population of Cuban exiles in Florida, a battleground state in USA elections.
The incident threatens to set back relations between the two countries, which President Barack Obama took major strides to fix in 2015.