In a series of bizarre purported incidents, U.S. officials say American diplomats in Cuba have suffered unexplained loss of hearing that might be caused by a covert acoustic device, according to The Associated Press.

Citing officials with knowledge of the investigation, the AP reports the trouble began in the fall of 2016. Several of the diplomats who suffered from the mysterious affliction were recent arrivals at the embassy and some had symptoms so severe they were sent back to the U.S. From there, the AP says:

After months of investigation, U.S. officials concluded that the diplomats had been exposed to an advanced device that operated outside the range of audible sound and had been deployed either inside or outside their residences. It was not immediately clear if the device was a weapon used in a deliberate attack, or had some other purpose.

In an unusually cryptic State Department press briefing Wednesday, department spokesperson Heather Nauert said two Cuban diplomats in the U.S. had been asked to leave in response to the incidents. But Nauert said the U.S. still wasn't sure what was behind the whole thing.

"We don't have any definitive answers about the source or the cause of what we consider to be incidents," she said. 

Later, there was this exchange with a reporter:

The same day, the Cuban foreign ministry posted a lengthy statement online, saying the U.S. informed the ministry in mid-February about the alleged incidents.

"Cuba took this issue with the utmost seriousness and acted expeditiously and professionally in order to clarify the facts of this situation, initiating a comprehensive, priority and urgent investigation on the indications of the highest level of the Cuban government," the statement said. "The Ministry categorically emphasizes that Cuba has never, nor would it ever, allow that the Cuban territory be used for any action against accredited diplomatic agents or their families, without exception. Moreover, it reiterates its willingness to cooperate in the clarification of this situation."

Cuba lodged a protest after its diplomats were expelled, the statement said.

A former veteran CIA officer told Code and Dagger it's not unusual for a less-than-friendly host nation to mess with American diplomats and spies abroad; Russians, for instance, are infamous for it. But in his lengthy career, he said he'd never seen anything exactly like this.

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Read: Associated Press Report

Primary Source: Cuban Foreign Ministry Statement