Washington (CNN) President Donald Trump said Monday that he does "believe Cuba is responsible" for the mysterious attacks that sickened at least 22 US diplomats and family members in Havana.

"I do believe Cuba's responsible, I do believe that," Trump said in the Rose Garden.

Investigators continue to examine the circumstances surrounding as many as 50 attacks that may have involved the use of an acoustic device, a US official has told CNN.

The device was so sophisticated, it was outside the range of audible sound, the official said. And it was so damaging, the source said, that one US diplomat now needs to use a hearing aid.

Three US officials told CNN that the device was deployed either inside or outside the residences of US diplomats living in Havana.

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