Story highlights US officials tell CNN they are still mystified by the incidents

In late 2016, US government workers began having strange symptoms

(CNN) The health incidents that sickened US diplomats in Cuba and further set back US-Cuban relations will be the subject of a Senate hearing on Tuesday. However, it's not expected to resolve the mystery of what some have alleged were "sonic attacks" amid a public disagreement between two Republican members of the committee holding the hearing over whether the diplomats were victims of "attacks."

"There are some people with symptoms happening that are unexplained," Sen. Jeff Flake, an Arizona Republican, told CNN on Friday during a trip to the island. "The Cubans bristle at the word 'attack.' I think they are justified at doing so. The FBI has said there is no evidence of an attack. We shouldn't be using that word."

Flake, a backer of improved US-Cuban relations and a member of the Senate Committee on Foreign Relations, which is holding the hearing, said he had received classified briefings that backed up Cuba's denials of involvement in the incidents.

Critics of the Cuban government said they must know more than they are letting on about what happened.

"It is impossible to conduct 24 separate & sophisticated attacks on U.S. Govt personnel in #Havana without the #CastroRegime knowing about it," Sen. Marco Rubio, a Florida Republican, shot back to Flake on Twitter. "Any U.S. official briefed on matter knows full well that while method of attack still in question, that attacks & injuries occurred isn't."

Read More