In this Oct. 3, 2017 photo, tourists ride a classic convertible car on the Malecon beside the United States Embassy in Havana, Cuba. The United States said Friday it was making permanent its decision last year to withdraw 60 percent of its diplomats from Cuba, citing the need to protect American personnel from what the State Department called "health attacks" that remain unexplained. (AP Photo/Desmond Boylan)

Citing mysterious "health attacks" in Havana, the United States said Friday 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 non-essential 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 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, forcing Cubans who wish to visit the United States to seek visas through U.S. embassies in other countries. The U.S. is also expected to fall far short of granting the 20,000 immigrant visas to Cubans that have been allotted annually for decades.

In Havana, hundreds of Cubans waited in line Friday outside the Colombian Embassy seeking visas to visit that country, from which they would have to apply for a separate visa at the American Embassy in Bogota to travel to the United States. Some slept under trees, having traveled to Cuba's capital from the provinces.

"This whole situation is making me very sad," said Ana Maria Velazquez, an accountant from neighboring Matanzas Province with two children in Florida. She had been waiting for her appointment with Colombian officials for three days. "There should be normal relations between the two countries, but if the U.S. doesn't want them, at least they should do something that doesn't hurt people."

Maria Angeles Reyes said she and her husband paid $1,400 for flights to Bogota and lodging there. "Those who are paying are ordinary Cubans," she said.

Secretary of State Rex Tillerson signed off on the permanent plan for reduced staffing out of concern for "the health, safety and well-being of U.S. government personnel and family members," the department said in a statement Friday.

"We still do not have definitive answers on the source or cause of the attacks, and an investigation into the attacks is ongoing," the department said.

Cuba has repeatedly denied either involvement in or knowledge of any attacks, and has said its own investigation into the illnesses has turned up no evidence of deliberate action. The United States has not accused Cuba of such action but has said Havana holds responsibility nonetheless, arguing that such incidents could not have occurred on the small, communist-run island without the knowledge of Cuban officials.

The mysterious case has sent U.S.-Cuba relations plummeting from what had been a high point when the two countries, estranged for a half-century, restored full diplomatic ties under President Barack Obama in 2015.

In late 2016, U.S. Embassy personnel began seeking medical care for hearing loss and ear-ringing that they linked to weird noises or vibrations—initially leading investigators to suspect "sonic attacks."

An interim FBI report disclosed by The Associated Press in early January said the investigation has uncovered no evidence that sound waves could have damaged the Americans' health. But Tillerson has said he's still convinced the diplomats were hit by deliberate, specific attacks targeting their health.

Doctors treating the patients said in a study published last month that the sounds heard by diplomats might have been a byproduct of something else that might help explain the full symptom list: memory problems, impaired concentration, irritability, balance problems and dizziness. The study in the Journal of the American Medical Association said doctors still have no clear diagnosis of just what happened to trigger the mysterious health problems.