DENVER -- A plane made an unscheduled stop in Denver after a passenger became unruly and had to be restrained by fellow passengers and flight attendants.

Southwest Flight 3655 was traveling from Chicago to Salt Lake City Monday evening when a male passenger got up and refused to sit down, said Southwest spokesman Paul Flaningan.

The passenger was near the front of the plane and refused the flight crew's repeated orders to return to his seat.

Several passengers had to help flight attendants restrain the man, who was held in the back of the plane until it landed at DIA, Flaningan said. No one was injured in the incident.

The pilots declared an in-flight emergency at about 8:30 p.m MST and asked to stop in Denver, where the flight was met by Denver police and the FBI, Flaningan said.

The man, who has not been identified, was released pending investigation, FBI spokesman Dave S. Joly said Wednesday.

A decision on whether to charge the suspect will be made once the investigation is completed and federal prosecutors review the case, Joly said.