HILLSIDE – Undercover FBI agents arrested an 18-year-old American man who tried to detonate what he believed was a car bomb outside a downtown Chicago bar, federal prosecutors said Saturday.

Adel Daoud, a U.S. citizen from the Chicago suburb of Hillside, was arrested Friday night in an undercover operation in which an agent pretending to be a terrorist provided him with a phony car bomb and watched him press the trigger, prosecutors said.

The U.S. Attorney's Office in Chicago, which announced the arrest Saturday, said the device was harmless and the public was never at risk.