Senate Intelligence Committee Chair Mark Warner, D-Va., said on Wednesday that the lack of information about the alleged “Havana Syndrome” that is reportedly affecting U.S. diplomats is “very problematic,” in an interview with Politico.

“The fact that we still don’t know for sure who did it and how these attacks were carried out is very, very problematic, to say the least. We are, in a bipartisan way, absolutely on top of this,” Warner told Politico Playbook during a virtual interview.

“I think that the administration, when they reach their conclusion, will lay that out,” he added to Politico. “The challenge will be, when they lay it out — particularly if it’s a nation-state that originates this activity — what we do then is going to pose one of the most challenging policy choices for this administration to date.”

Over 200 American personnel, including diplomats and members of the CIA, have reported similar symptoms that have been dubbed “Havana Syndrome,” after the phenomenon was first observed in Cuba. A Biden administration official previously told Politico that the U.S. intelligence community is actively investigating the cause of the incidents.

“We are determined to get to the bottom of this as quickly as possible,” said the official, who was not named, earlier this month to Politico. “The [intelligence community] is actively examining a range of hypotheses, but has made no determination about the cause of these incidents or who is responsible.”

Warner on Wednesday faulted the Trump administration for not getting to the bottom of the issue after it was first reported in 2016.

“This is an area where the previous administration just whiffed,” he told Politico. “I was very disappointed that, for example, at the CIA and at [the] State Department and at [the Defense Department], that employees — career employees who are victims of these attacks — weren’t treated seriously enough, literally for years.”