"At this point, at this moment, we don't know the cause of these incidents, which are both limited in nature and the vast majority of which have been reported overseas," said White House press secretary Jen Psaki, acknowledging the newly reported cases in the U.S.
The Biden administration has launched a review of U.S. intelligence to determine if there are other previously unreported cases and if there is a "broader pattern," a National Security Council spokesperson confirmed to ABC News.
Last month, U.S. defense officials briefed lawmakers on the Senate and House Armed Services Committees on several previously unreported incidents of U.S. personnel falling sick after alleged exposures, congressional sources confirmed to ABC News.
Dozens of Americans have been diagnosed with a range of symptoms, including traumatic brain injuries, with several describing bizarre experiences like strange noises and sensations. The U.S. government has acknowledged cases in Cuba, China, Uzbekistan and Russia -- but there are media reports of other countries now, too.
The issue has vexed U.S. officials since 2016, when the first cases were reported at the embassy in Havana. While there's still no definitive answer, the National Academies of Science in December issued a report, commissioned by the State Department, that concluded the most likely source is "directed, pulsed radio frequency energy."
Among the possible new cases are also reportedly at least two incidents in the Washington area, according to GQ magazine, CNN and others. ABC News has not independently verified those reports.
While Warner and Rubio praised President Joe Biden's CIA director, Bill Burns, for his "renewed focus on these attacks," other lawmakers have become publicly exasperated with the executive branch's response.
During a Senate hearing last week, Sen. Jeanne Shaheen, D-N.H., criticized the U.S. intelligence community's "clamp down on information that's available to Congress, that's available to the public."
That, in turn, has led to a growing number of reports of alleged incidents without clarity about whether or not they're related to what's happened to U.S. personnel in Cuba, Shaheen said.
"It's not clear whether the information we're getting is correct or incorrect," she told Director of National Intelligence Avril Haines. "The horse is out of the barn on this. The information is already out there, and I think it behooves us all to try to make sure that the information that gets out is accurate and that people understand what's happening."
Beyond Cuba, the State Department has previously acknowledged incidents in China, Uzbekistan and one redacted country in an internal report that was declassified and released in February. That unknown country is likely Russia, where a former CIA official said he was attacked.
That official, Marc Polymeropoulos, told ABC News in March that he's now receiving treatment at Walter Reed Medical Center for a traumatic brain injury as well.
But after reports of possible incidents in Syria, the head of U.S. Central Command said he had no evidence that was true.
"I have found no evidence of those attacks" in CENTCOM's region, which includes Syria, Gen. Frank McKenzie, CENTCOM commander, told a Senate panel in April. During the same hearing, Gen. Stephen Townsend, head of U.S. Africa Command, added he's "not seen that phenomenon in Africa" either.
One law enforcement source dismissed speculation about one incident in the Washington area, telling ABC News, "There is no credible evidence to support this."
Biden's National Security Council is now conducting "a full review of intelligence reporting to ascertain whether there may be previously unreported incidents that fit a broader pattern," a spokesperson confirmed to ABC News Friday.
While the Trump administration initially said affected personnel had suffered "health attacks," the spokesperson added that whether the incidents are an attack and whether they're the work of a foreign actor are still under "active inquiry."
ABC News' Mike Levine, Trish Turner and Benjamin Siegel contributed to this report.