A recording that reveals the sound of a sonic weapon said to have been used against US embassy staff in Cuba has been released.
The high-pitched frequencies are believed to have injured at least 22 diplomatic staff, who suffered problems with hearing, cognitive function, vision, balance and sleep.
The allegations have caused relations between the two countries to deteriorate significantly, just over a year after former President Barack Obama made a historic trip to the Caribbean island.
Earlier this month, 15 Cuban diplomats were expelled from the communist government’s embassy in Washington, DC.
Any sound played at normal levels is not thought to be harmful to humans but the affected staff said they heard it played at high levels – through what device is unknown.
The recordings from Havana have been sent for analysis to the US Navy, which has advanced capabilities for analysing acoustic signals, and to the intelligence services, the Associated Press reported.
A closer examination of one recording revealed it was not just a single sound. Roughly 20 or more different frequencies, or pitches, are embedded in it, according to reports.
To the ear, the multiple frequencies can sound a bit like dissonant keys on a piano being struck all at once. Plotted on a graph, the Havana sound forms a series of "peaks" that jump up from a baseline, like spikes or fingers on a hand.
"There are about 20 peaks, and they seem to be equally spaced. All these peaks correspond to a different frequency," said Kausik Sarkar, an acoustics expert and engineering professor at the George Washington University, who reviewed the recording with the AP.
But the recordings have not significantly advanced US knowledge about what is harming diplomats in Cuba and the US government has not officially blamed anyone.
The island’s government, led by Raul Castro, has denied involvement or knowledge of the attacks.
But US officials believe more could be done to prevent them.
"We believe that the Cuban government could stop the attacks on our diplomats," said John Kelly, White House chief of staff.
On the street in Havana, the reaction among locals was markedly different, with many people mocking the allegations, citing the tense relations between the US and Cuba.
"It isn't the first or the last excuse that they invent to discredit Cuba and its leaders," said lawyer Alexander Tamame, 36. "I don't think anything really happened."
Agencies contributed to this report
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