The report comes a day after the U.S. expelled two Cuban diplomats after a number of United States embassy staff were forced to leave Havana because of unspecified medical symptoms that were first reported in 2016.
US officials believe a group of American diplomats in Havana suffered severe hearing loss after being exposed to a covert sonic device.
Cuba employs a state security apparatus that keeps many people under surveillance and USA diplomats are among the most closely monitored people on the island.
It also led to the expulsion of the Cuban diplomats from the US back in May.
Officials, speaking under condition of anonymity, said an investigation revealed that the diplomats had been affected by a device emitting noises outside the range of audible sound.
Additional U.S. action could follow if the investigation points to the Cuban government being culpable for what happened to the U.S. employees, officials said.
Earlier in the day, the U.S. Department of State made a vague statement insinuating foul play by the government of Cuba. "We're taking this incident very seriously, and it's under investigation right now".
"We first heard of these incidents back in late 2016", State Department spokesperson Heather Nauert said. While they were not life-threatening, she revealed that a number of people had been brought home to the USA as a result.
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According to BBC, it is clear that the two Cuban diplomats left Washington in May.
"Some of our people have had the option of leaving Cuba as a result, for medical reasons", she said.
An exterior view of the U.S. Embassy is seen in Havana, Cuba, June 19, 2017.
US officials told The Associated Press that about five diplomats, several with spouses, had been affected and that no children had been involved.
An investigation to find out what happened is now underway by the FBI and Diplomatic Security Service.
Relations between the United States and Cuba were restored in 2015 after a half-century break by then-president Barack Obama and his Cuban counterpart Raul Castro. However, things change when on April 13, 2015, President Barack Obama announced that he would lift some longstanding restrictions placed on Cuba, allowing Cuban Americans to visit and send remittances to their families and easing - but not removing - the 47-year-old economic embargo on the island nation.
"The Ministry of Foreign Affairs reaffirms that Cuba complies strictly and seriously with its obligations under the Vienna Convention on Diplomatic Relations of 1961 regarding the protection of the integrity of diplomatic agents and the premises of the mission", the ministry added.