A man in Ohio has been accused of joining al-Qaeda and plotting to bomb targets in the US and overseas.
The FBI's Patrick Murphy said the investigation had taken four years
Christopher Paul, 43, faces charges of providing material support to terrorists and conspiracy to use a weapon of mass destruction.
He allegedly went to terror training camps in Afghanistan and Pakistan and trained "co-conspirators" in Germany.
Mr Paul was due to appear in court in Columbus, Ohio, on Thursday. He has not yet responded to the charges.
The 14-page indictment issued by a federal grand jury lists US embassies, military premises and consular buildings in Europe as examples of buildings that might have been targeted, as well as resorts frequented by US tourists.
It also says Mr Paul trained in the "use of assault rifles, grenades, rocket-propelled grenades, small unit tactics and hand-to-hand tactics" while at terror training camps in Pakistan and Afghanistan in 1990.
The document does not say whether any of the suspected plots were ever carried out.
FBI agent Tim Murphy told the Associated Press news agency that the investigation had spanned four years, three continents and at least eight countries.
Assistant US Attorney General Kenneth Wainstein said in a statement: "The indictment of Christopher Paul paints a disturbing picture of an American who travelled overseas to train as a violent jihadist, joined the ranks of al-Qaeda and provided military instruction and support to radical cohorts both here and abroad."
If tried and found guilty, Mr Paul would face a maximum penalty of life imprisonment.