WASHINGTON (AP) — The Biden administration is investigating a recent rash of mysterious health incidents reported by American diplomats and other government employees in Vienna, Austria, U.S. officials said Friday.

Some of the symptoms are similar to those first reported by U.S. diplomats and spies in Havana, Cuba, in 2016 and 2017 for which no definitive cause has yet been determined, according to the officials, who said more than 20 new cases were being looked at by medical teams at the State Department and elsewhere, including the Pentagon and CIA.

“In coordination with our partners across the U.S. government, we are vigorously investigating reports of possible unexplained health incidents among the U.S. Embassy Vienna community,” the State Department said. “Any employees who reported a possible UHI received immediate and appropriate attention and care.”

Some believe the unexplained injuries, which include brain damage, are the result of attacks with microwave or radio wave weapons. However, despite years of study there is no consensus as to what or who might be behind the incidents or whether they are, in fact, attacks.

The Vienna-based employees have reported suffering from mysterious symptoms since President Joe Biden was inaugurated, according to the officials. The Vienna cases were first reported Friday by The New Yorker magazine.

Vienna has for centuries been a center for espionage and diplomacy and was a hub for clandestine spy-versus-spy activity during the Cold War. The city is currently the site of indirect talks between Iran and the United States over salvaging the nuclear deal that was negotiated there in 2015.

Those talks are now in hiatus and it was not immediately clear if any members of the U.S. negotiating team were among those suffering from injuries.

The problem has been labeled the “Havana Syndrome,” because the first cases affected personnel in 2016 at the U.S. Embassy in Cuba. In May, officials said at least 130 cases across the government are were under investigation, up from several dozen last year.

People who are believed to have been affected have reported headaches, dizziness and symptoms consistent with concussions, with some requiring months of medical treatment. Some have reported hearing a loud noise before the sudden onset of symptoms.

Particularly alarming are revelations of at least two possible incidents in the Washington area, including one case near the White House in November in which an official reported dizziness.

Although some are convinced the injuries are the result of directed energy attacks, others believe the growing number of cases could actually be linked to “mass psychogenic illness,” in which people learning of others with symptoms begin to feel sick themselves.