Yesterday, US State Department spokeswoman Heather Nauert told reporters that the exact nature of the incidents was unclear, but Americans serving in Cuba had returned to the US for non life-threatening "medical reasons".
Despite ostensibly improved ties between the USA and Cuban governments, the State Department on Wednesday confirmed it had expelled two Cuban diplomats from Washington because of an "incident" in Havana that harmed US personnel there.
A spokesperson for the State Department's Bureau of Western Hemisphere Affairs says the department does not have "definitive answers on the source or cause of the incidents".
"The safety and security of US 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".
Citing an anonymous government official, CNN reports that the United States is still investigating the possibility this was an attack by a third country that might be trying to harm America's relations with Cuba.
It comes a day after the United States said its diplomats in Havana were experiencing unusual physical symptoms.
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.
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However, the Associated Press, citing unnamed sources, reported Wednesday that the symptoms included hearing loss, which in some cases is believed to be permanent.
The U.S. first learned of the medical issues towards the end of 2016, more than a year after the U.S. reopened its embassy in Havana.
Two Cuban officials in Washington were asked to leave the U.S.in May as a result of the incidents.
Nauert confirmed during Wednesday's briefing that the investigation is ongoing and authorities are still trying to determine what afflicted US Embassy staffers. It appeared that she was saying that because some of our diplomats came home, some Cuban diplomats had to leave as a matter of reciprocity.
However, officials familiar with the probe said investigators were looking into the possibilities that the incidents were carried out by a third country such as Russian Federation, possibly operating without the knowledge of Cuba's formal chain of command. "Under the Vienna Convention, Cuba has an obligation to take measures to protect diplomats". "We take those incidents very seriously and there is an investigation now underway".
President Trump announced a couple of months ago he was rolling back numerous advances with Cuba that Obama had overseen. Some had to go to the U.S. for treatment and one is thought to have become permanently deaf.
It is understood that the two expelled Cuban diplomats left Washington DC in May, the BBC's Will Grant reports from Havana.
The Cuban government said in a lengthy statement late Wednesday that "Cuba has never permitted, nor will permit, that Cuban territory be used for any action against accredited diplomatic officials or their families, with no exception".