The so-called sonic attacks are believed to have started in November last year, having affected more diplomatic personnel than it was previously disclosed, CNN reports. Two senior U.S. government officials, who did not want to be identified, told the network that more than 10 diplomats and their families had to be brought back to the U.S. for medical treatment. Others decided to leave their assignments at the embassy in Havana to prevent further health damages.

One of the victims of the sonic attacks will have to use hearing aid from now on, the two sources told CNN. Following the departure of the American diplomats for medical treatment, the U.S.

State Department demanded two diplomats from the Cuban embassy in Washington to leave until everything is clarified. Canadian diplomats have also been affected by the attacks.

FBI investigation: Third country may be involved

The Cuban government denies any participation in the attacks. It has begun an investigation to sift through the facts. Up to now, though, nothing has been clarified. The country’s authorities have also reinforced security in the zone where the attacks carried out.

In an unprecedented move, the Cuban government authorized the FBI and the Royal Canadian Mounted Police to conduct their own investigations on the island. As of now, no sonic device that can have caused the health damages was found at the houses of American and Canadian diplomatic personnel in Cuba.

The ongoing investigations are aiming to determine whether the attacks were carried out by operatives from third-party countries, especially from those with conflicting relationships to the United States, such as Iran, Venezuela, China, Russia and North Korea.

A solution for the Cuba mystery

According to CNN, the attacks occurred when the diplomats and their families were at home.

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Most of the times, the sonic devices operate outside the range of audible sound, with the attacks handled either inside or outside the buildings. Other times, the devices produce deafening noises, resembling the sound of metal scratching. In both situations, affected people instantly felt unwell. Nausea, headaches, and hearing loss have been known to occur.

Cuba and the United States have restored diplomatic relations on 20 July 2015, following a long period without ties that begun in 1961. The rapprochement with Cuba was led by former President Barack Obama. Now, the ‘acoustic warfare’, which resembles old spy tricks from the cold war, can undermine the yet unstable relations between the two countries [VIDEO].