The noise heard by some American diplomats who were affected by mysterious health attacks in Havana was a shrill, almost cricket-like tone with an electrical whine, according to a recording of the sound obtained by The Associated Press.

The recording is one of several reviewed by the AP, with the recordings made under "different circumstances." According to the news organization, it's just one of the sounds documented in Cuba that led U.S. investigators to initially suspect that some kind of covert sonic device was responsible for causing symptoms in American diplomats ranging from permanent hearing loss to difficulty sleeping to balance problems.

Not all of the Americans who reported experiencing the mysterious symptoms while in Cuba heard the sound. However, some of those affected confirmed to the AP that the noise on the recording is what they heard.

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Heather Nauert, a State Department spokeswoman, said Thursday that she could not authenticate the recording published by the AP, and reiterated that the U.S. investigation into the attacks is ongoing.

"An investigation is still underway. We don’t know who or what is responsible for it,” she said at a press briefing. "We can not authenticate the tape in any way."

The recordings taken in Havana have been handed over to the U.S. Navy and intelligence services for analysis, the AP reported. But according to the news wire, the sounds have not significantly advanced U.S. investigators' understanding of the attacks or who is behind them.

Back at the U.S. Embassy in Havana, the sounds have been played for American personnel to make them aware of the noise. U.S. workers have been told that, if they hear the sound, they should immediately seek to move away from it, the AP reported.

The health attacks began in the fall of 2016 and were believed to have stopped in March of this year. But the State Department revealed last month that the attacks had happened as recently as August.

So far, the U.S. government has confirmed that 22 Americans have been affected by the attacks, though that number could rise. The attacks are considered "ongoing," and the U.S. and Cuba are conducting separate investigations.

The Cuban government has repeatedly denied any responsibility for the attacks, and is said to be cooperating with U.S. investigators looking into the matter. The country's foreign ministry has noted that it has allowed the FBI to work on the ground in Cuba for the first time in more than 50 years.

According to the AP, Cuban officials declined to say whether the U.S. had shared the recordings with the Cuban government.

But the Trump administration announced late last month that it would cut the U.S. diplomatic presence in Havana by about 60 percent — a move it said was necessary to guarantee the safety of American personnel. Days later, it ordered 15 Cuban diplomats in Washington to leave.

State Department officials have said that the diplomatic withdrawal is not intended as a punitive measure, but have instead argued that the Cuban government has simply not been able to reassure the U.S. that Americans are safe in Havana.