The United States is reportedly still trying to explain how at least 21 diplomats working in Cuba suffered sudden brain injuries that include hearing loss and speech problems.

Officials from the FBI, the State Department and other U.S. intelligence agencies are at a loss as to what the possible weapon could be and are working to make sense of the physics, The Associated Press reported Thursday.

One American diplomat in Havana described what some are calling “health attacks,” in which he heard a "blaring, grinding noise" from his bed — but when he moved only a few feet away, he stepped into silence, almost like an "invisible wall cutting straight through his room," the AP described.

ADVERTISEMENT

Some of the injuries took place in confined rooms or even certain areas of rooms, the news wire reported, pointing to an astounding level of precision in which the attacks occurred.

The injuries vary in severity, with some who sustained more serious brain damage than previously realized, the news wire reported. Stories of how the injuries came about also largely differ with some hearing different noises in real time, while some did not hear or notice anything before their symptoms appeared. The victims also are experiencing different symptoms, which is making the search to identify a culprit so difficult.

The device used in the attacks has still not been identified, the AP reported, citing interviews with over a dozen current and former U.S. officials, Cuban officials and others briefed on the investigation who spoke to the news wire anonymously.

The U.S. government first acknowledged the attacks in August, after the State Department expelled two Cuban diplomats from the U.S. over safety concerns of American officials experiencing said symptoms — nine months after the injuries were first reported.