WASHINGTON — Citing mysterious “health attacks” in Havana, the United States says it is making permanent its withdrawal of 60 percent of its diplomats from Cuba, extending an action that has hurt the island nation’s economy and cramped Cubans’ ability to visit the U.S.

Last October, the State Department ordered nonessential embassy personnel and the families of all staff to leave Havana, arguing the U.S. could not protect them from unexplained illnesses that have harmed at least 24 Americans. But by law, the department can only order diplomats to leave for six months before either sending them back or making the reductions permanent.

The six months expire Sunday. So the department said Friday it was setting in place a new, permanent staffing plan that maintains a lower level of roughly two-dozen people — “the minimum personnel necessary to perform core diplomatic and consular functions.” The department also said that the embassy in Havana would operate as an “unaccompanied post,” meaning diplomats posted there will not be allowed to have spouses or children live with them in the country.

The downsizing of the embassy staff — and a travel warning the U.S. issued warning Americans to reconsider travel to the island — have had significant effects for Cuba’s economy and for its citizens. With fewer employees on hand, the U.S. Embassy in Havana halted visa processing.