UNITED NEWS INTERNATIONAL (UNI) — The U.S. has created a task force to investigate a series of mysterious health incidents and so-called “sonic attacks” that have affected U.S. diplomats.

U.S. Secretary of State Mike Pompeo said June 5 that the Health Incidents Response Task Force was established last month in the wake of these unexplained health issues.

Twenty-four U.S. diplomats fell ill in Cuba beginning in the fall of 2016, reporting symptoms ranging from severe headaches to concussions to permanent hearing loss.

The incidents in Cuba seemed to stop after August of last year. However, last month, a staffer at a U.S. consulate in China reported similar symptoms.

In both cases, the exact cause of these symptoms remains unclear.

However, U.S. officials have said these symptoms could be the result of a “sonic attack,” in which a hidden high-pitched device is placed somewhere in or near the embassy.