The mysterious and sudden brain injuries suffered by a small group of American diplomats and spies overseas were most likely caused by pulsed electromagnetic energy delivered by an external device, a panel of scientific experts working for U.S. intelligence agencies has concluded.

The panel’s findings, while full of caveats, are consistent with what has been a longstanding hypothesis by intelligence officials — that a foreign adversary, most likely Russia, is responsible for at least some of the symptoms suffered by those who have fallen victim to what is commonly known as Havana Syndrome.