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MIAMI (CBSMiami) –  Doctors discovered brain abnormalities while treating victims of a sonic attack in Cuba, according to the Associated Press.

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The mysterious attacks targeted embassy workers on the island nation.

American classic cars are seen outside the US Embassy in Havana on August 14, 2015.(ADALBERTO ROQUE/AFP/Getty Images)

According to the report, several U.S. officials said medical testing revealed embassy workers developed changes to the white matter tracts that let different parts of the brain communicate.

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Victims have reported damages in their hearing, vision, balance and their memory.

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Secretary of State Rex Tillerson addressed the report during a news conference in Belgium.

“What we’ve said to the Cubans is, small island, you got a sophisticated security apparatus, you probably know who is doing it. You can stop it. It’s as simple as that. So that’s what we’ve asked the Cubans. We understand the Cubans don’t like the actions we’ve taken. We don’t like our diplomats being targeted,” said Tillerson.

It is the most specific finding to date about physical damage from the attacks.

The finding is also one of several factors fueling growing skepticism that some kind of sonic weapon was involved.

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Back in October, Cuban officials aired a special denying the attacks. The special, titled “Alleged Sonic Attacks,” claims the recordings presented to them by the U.S. sounds like crickets.