"United flight 972 from Chicago to Brussels returned Friday to Chicago due to a suspected security concern," the airline said in a statement.
United Flight 972 was scheduled to depart from O'Hare around 6p.m Friday and arrive in Brussels around 9 a.m.. The flight landed in Chicago at 10:07 pm, where it was met by law enforcement, the airline said.
There were 228 passengers onboard, according to the airline.
"We are accommodating passengers on an alternate flight to Brussels," the airline said.
FBI spokeswoman Joan Hyde said her agency responded to the diverted flight, but no arrests were made.
Tribune reporter Rosemary Regina Sobol contributed to this report.