The Federal Bureau of Investigation is currently investigating what appears to be an attack on U.S. diplomats working in Cuba involving a covert sonic weapon. Last fall, a number of diplomats with the newly-opened U.S. embassy in Havana began to suffer an unexplained loss of hearing, forcing many of the afflicted diplomats to return home for medical treatment. Diplomatic ties were re-opened between Cuba and the U.S. in 2015, following decades of tension between the two countries.

An investigation into the incident concluded that five diplomats were affected by a sonic device that operated outside the range of human hearing, placed either outside or inside their residences. The investigation wasn’t able to determine if the diplomats were the target of the attack, or if the effect was unintentional.

The State Department responded by expelling two Cuban diplomats last May. "We requested their departure as a reciprocal measure since some U.S. personnel’s assignments in Havana had to be curtailed due to these incidents," according to spokesperson Heather Nauert. "Under the Vienna Convention, Cuba has an obligation to take measures to protect diplomats."

The Cuban government denies being behind the attacks, and has launched their own investigation into the matter, asserting that "Cuba has never, nor would ever, allow the Cuban territory to be used for any kind of action against accredited diplomats or their families."

U.S. investigators are also looking into the possibility of the attacks having been perpetrated by a third party. Global Affairs Canada has also announced that a number of Canadian diplomats have also been affected with symptoms similar to their U.S. counterparts.