HAVANA — The Associated Press has learned that frightening attacks on U.S. personnel in Havana struck the heart of America’s spy network in Cuba, with intelligence operatives among the first and most severely affected victims.

Individuals familiar with the situation said it wasn’t until U.S. spies working under diplomatic cover reported hearing bizarre sounds and experiencing even stranger physical effects that the United States realized something was wrong.

The attacks started within days of President Donald Trump’s surprise election in November. Yet the precise timeline remains unclear, including whether intelligence officers were the first victims hit or merely the first victims to report it.

The U.S. calls the situation “ongoing.”