Secretary of State Rex Tillerson's team isn't ready to blame Raul Castro's regime for the mysterious ailments afflicting U.S. government personnel working in Cuba.

"This is a situation that we're still assessing," State Department spokeswoman Heather Nauert told reporters. "When I say an active investigation is under way, in part what that means is, we don't know exactly where this came from. We can't blame any one individual or a country at this point yet."

A number of American personnel deployed to Havana after the reopening of the U.S. embassy there began to suffer physical ailments, beginning in late 2016. Nauert declined to confirm the details of the symptoms, which was reportedly hearing loss that may have been caused by an "acoustic attack" on the State Department employees. Some of the victims have returned to the United States, and Tillerson's team sent two Cuban diplomats home.

Nauert emphasized that Cuba had a responsibility under international conventions to guarantee the security of the U.S. personnel. "Our Americans were not safe, they were not secure, obviously, because something has happened to them," she said.

She declined to say if the incidents would cause President Trump to reverse the diplomatic reopening that former President Barack Obama initiated with Cuba in his second-term.

"I don't have any information on that particular part for you," she said.

Sen. Marco Rubio, R-Fla., one of the leading Cuba hawks in Congress, has blamed the Cuban government directly and argued the incident shows the Obama policy failed to improve relations or deter harassment.

"This has not stopped with President Obama's appeasement," Rubio said Wednesday. "Personal harm to U.S. officials shows the extent the Castro regime will go and clearly violates international norms."