ILLINOIS, USA (AP) — 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 yesterday.

Adel Daoud, a US 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 US Attorney's Office in Chicago, which announced the arrest yesterday, said the device was harmless and the public was never at risk.

Daoud is charged with attempting to use a weapon of mass destruction and attempting to damage and destroy a building with an explosive. He remains in custody pending a detention and preliminary hearing set for tomorrow in federal court.

A person who answered the phone at the home where Daoud and his family live and identified herself as his sister, Hiba, declined to discuss Daoud, the family or the arrest.

"We don't even know anything. We don't know that much. We know as little as you do," she said. "They're just accusations. ... We'd like to be left alone."

The FBI began monitoring Daoud after he started using an email account to get and distribute material about violent jihad and the killing of Americans, prosecutors said.

In May, two undercover FBI agents contacted Daoud in response to the material and exchanged electronic messages with him in which he expressed an interest in violent jihad in the United States or abroad, according to an affidavit by an FBI special agent.