The State Department’s Accountability Review Board will sort through what officials said was a mountain of confounding and conflicting evidence, some of it classified. Steve Goldstein, the undersecretary of state for public affairs, rejected Mr. Rubio’s accusation that the department had violated the law around review boards.
“We believe we have the authority to determine when the Accountability Review Board is set in place,” Mr. Goldstein said. He added that the department was no closer to determining the cause of the illnesses than it was when the inquiry began.
“We believe that the Cuban government knows what occurred,” he said. “So what we’d like to them to do is tell us what occurred.”
After the embassy staff members fell ill, Mr. Trump expelled 15 Cuban diplomats from the United States, the most serious of a series of actions he has undertaken to unwind the new diplomacy between the countries that was opened by President Barack Obama.
An F.B.I. report issued last week, first reported by The Associated Press, has since concluded that a sonic weapon was probably not used to sicken the embassy personnel, disputing what medical experts have said for months. A viral attack remains a possibility, said Todd Brown, a State Department security official.
Among the symptoms reported by the embassy personnel are sharp ear pain, dull headaches, tinnitus, vertigo, disorientation, nausea and extreme fatigue. Some have been diagnosed with mild brain injuries similar to what might happen from a concussion.
On Tuesday, Dr. Charles Rosenfarb, the State Department’s medical director, dismissed the notion that the problems resulted from some form of mass hysteria.
“The objective tests that were done were not ones that basically were easily faked,” Dr. Rosenfarb said, adding that the “findings suggest this is not a case of mass hysteria.”
In November 2016, American diplomats and their family members in Havana first began experiencing what they later said were high-pitched beams of sound that they described as sometimes incapacitating. In some cases, the Americans reported feeling intense pressure in one ear. Initially, the pain was experienced in the homes of employees; it was later reported in hotel rooms as well.
The embassy’s charge d’affairs was finally told about these problems in late December 2016, and by January the alarm had spread through the upper reaches of the State Department in Washington. The United States informed Cuban officials of the problems in February, and Mr. Tillerson was briefed soon after he was confirmed that month, officials said.
The department initially tested 80 people, 16 of whom were found to have problems. Officials said the attacks appeared to occur consistently between November 2016 and March 2017, becoming sporadic that April and appearing to stop altogether around May. Two more bouts were reported in August, but none since then. Altogether, 24 people have since been identified as affected.
Senator Robert Menendez, Democrat of New Jersey, criticized the State Department’s initial response to the reports of illnesses as “bureaucratic, inadequate and troubling.”
By contrast, Senator Ron Johnson, Republican of Wisconsin, told department officials, “Seemed like you hopped on this pretty quick.”
In what he regarded as one of his administration’s greatest foreign policy legacies, Mr. Obama sought to end the hostility and mistrust that had characterized the relationship between Cuba and the United States for more than a half-century. That legacy has been partly reversed by the Trump administration in an effort to court voters who oppose the government in Cuba, but the problems reported by people at the American Embassy in Havana have also had a chilling effect on relations.