In Cuba, an acoustic attack may be to blame for severe hearing loss among U.S diplomats last year, though officials are uncertain of the cause the injuries.
A series of "bizarre" incidents attributed to a "covert sonic device" led to several U.S diplomats experiencing unexplained hearing losses, The Associated Press reported.
Two Cuban diplomats have since been expelled from the U.S, confirmed State Department officials on Wednesday, although specific details surrounding the incident remain vague.
"Some U.S. government personnel working at the embassy in Havana, Cuba, on official duty, working on behalf of the U.S embassy there, have reported some incidents that have caused a variety of physical symptoms," State Department spokeswoman Heather Nauert told reporters.
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.
"Some of our people have had the option of leaving Cuba as a result, for medical reasons," she said. "I can't tell you the exact number … but we had to bring some Americans home or some Americans chose to come home as a result of that. And, as result of that, we have asked two Cubans to leave the United States and they have."
An official told CNN that some of the employees affected could have suffered permanent 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 Cuban government had been alerted to the incidents and medical care has been provided to people experiencing these physical symptoms however, the State Department claims it has not been able to establish the exact cause of this.
"It can be quite serious," one official told CNN. "We have worked with the Cubans to try and find out what is going on. They insist they don't know, but it has been very worrying and troublesome."
In a statement, the Ministry of Foreign Affairs of Cuba said it took the issue seriously and acted in a professional manner in an attempt to clarify facts surrounding the situation by launching an investigation.
"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," the ministry 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."