Supporters of the three men disputed the charges, saying the men had come to protest at the Nato summit peacefully and that the police had confused beer-making equipment with explosives.
A lawyer for the three, Michael Deutsch, said undercover police officers had entrapped them by infiltrating the group and encouraging the bomb-making effort. The Chicago police department declined to comment on the tactics employed in the case.
The Cook County state attorney’s office said the three men had other weapons including a mortar, knives and a hunting bow. It said they considered attacking police stations and cars in Chicago to disrupt police operations for the two-day Nato summit that begins on Sunday.