Enlarge / Picture of the US embassy in Havana, taken on September 29, 2017 after the United States announced it is withdrawing more than half its personnel in response to mysterious health attacks targeting its diplomatic staff. (credit: Getty | ADALBERTO ROQUE)

More than half of the staff at the American Embassy in Havana, Cuba will return to the US in the wake of mysterious attacks that left diplomats with hearing damage and brain injuries, the State Department announced Friday.

The department said that the staff drawdown was necessary to ensure their safety. And “because our personnel’s safety is at risk, and we are unable to identify the source of the attacks, we believe US citizens may also be at risk and warn them not to travel to Cuba,” the department added in a travel advisory.

The attacks have injured 21 Americans associated with the embassy so far, as well as Canadian diplomats. Attacks took place in the diplomats’ homes as well as hotels. The last attack occurred in August, according to the New York Times.