New intelligence about weapons research by American adversaries opens the possibility of a foreign actor behind the mysterious incidents that have injured hundreds of U.S. personnel serving overseas.

WASHINGTON (Reuters) - A majority of U.S. intelligence agencies have reaffirmed in an updated assessment that it is "very unlikely" that a foreign adversary was responsible for so-called Havana Syndrome ailments, a U.S. intelligence official said on Friday.

Five agencies concluded it was unlikely a foreign adversary was behind the incidents, while two came to a different conclusion.