State Department officials have decided they will not punish Cuba by forcing the country to reduce its own diplomatic staff in Washington, a decision that was immediately attacked by Senator Marco Rubio, a Republican from Florida who fiercely opposed President Barack Obama’s decision to improve ties with Cuba.
Senator Patrick Leahy, a Democrat from Vermont, said punitive measures would only play into the hands of the attackers. “Whoever is doing this obviously is trying to disrupt the normalization process between the United States and Cuba,” Mr. Leahy said. “Someone or some government is trying to reverse that process.
Friday’s announcement came just three days after Mr. Tillerson met with Bruno Eduardo Rodríguez Parrilla, Cuba’s foreign minister, in Washington, in a meeting that the Cuban government requested. That meeting failed to persuade Mr. Tillerson that the Cubans could guarantee the safety of the remaining American employees in Havana, prompting him to decide to pull much of the embassy staff.
The staff remaining will carry out only emergency services, such as tasks to help United States citizens in need. Routine visa functions for Cuban citizens will no longer be conducted in Havana. Officials may soon direct Cubans seeking to travel to the United States to apply for visas at embassies or consulates in other countries.
American officials will continue to meet with their Cuban counterparts — but not in Cuba — until the cause of the attacks is uncovered, officials said. The most recent attack occurred in August.
Mr. Tillerson had been considering closing the embassy, which had only recently reopened after decades of frosty relations between the two countries. But one of the reasons Mr. Tillerson will keep it open is a growing belief among American officials that the Cuban government was probably not responsible for the attacks.
A former senior American official said there was information that the Cubans were rattled by what had happened and were desperate to find the cause. A third country may have been responsible, the official said.
The official said that the F.B.I. had visited the homes of diplomats in Cuba and had not been able to detect anything. The F.B.I. has also reviewed security footage of the homes and found nothing suspicious. The F.B.I. has been unable to duplicate the effects the diplomats have experienced in a lab.
That the Cubans offered to let the F.B.I. go to Havana and investigate represented a rare level of openness and was seen as yet another indicator that the Cubans themselves have been shaken by the incident.
American officials have speculated that the problems may have resulted from some sort of sonic attack or perhaps a surveillance operation gone wrong. The attack may have been the work of a country like Russia or rogue government unit. The fact that a Canadian diplomat was also affected has deepened the mystery. Relations between Canada and Cuba have long been warm.
The Trump administration has already reversed crucial pieces of what President Trump has called a “terrible and misguided deal” with Cuba that was struck during the Obama administration by reinstating travel and commercial restrictions on Cuba.
But the administration seems to have little appetite for entirely undoing other measures that are broadly popular, including among Republicans, such as allowing direct flights and cruises between the United States and Cuba, and rules making it easier for American companies to do business in Cuba.
Mr. Tillerson has long said that the safety of American diplomats is his top priority, and he is known to start every meeting of his senior staff by asking whether everyone is safe. However, nearly nine months into his tenure, Mr. Tillerson has yet to get someone nominated to lead the Bureau of Diplomatic Security, part of the State Department charged with safeguarding American diplomats around the world.