A bomb discovered at an ethanol plant in Peoria, Illinois, prompted the evacuation of more than 5,000 people Friday as local and federal authorities launched an investigation into the credible threat.

The device was found at the BioUrja Renewables facility, prompting officials to establish a one-mile evacuation zone covering parts of Peoria and neighboring East Peoria.

Peoria Mayor Rita Ali confirmed the discovery late Friday, saying authorities had identified a bomb but did not know whether additional devices were present.

Police Chief Brad Dixon said the plant first notified authorities of the threat shortly after 1 p.m. Friday. Bomb technicians rendered the suspicious package safe at approximately 9:12 p.m., but officials said the facility had not yet been cleared.

“It’s a large facility. There’s going to be an exhaustive search of the facility,” Dixon said during an early Saturday news conference.

The FBI is assisting local and state authorities with the investigation. Ryan Presley, special agent in charge of the FBI’s Springfield office, said investigators would work to identify those responsible.