Cologne on Friday condemned violence at the club's Europa Conference League game against Nice in southern France that left one fan in critical condition and dozens of others injured.
"We condemn the horrific scenes that took place before yesterday’s game in Nice in the strongest possible manner," club president Werner Wolf said in a statement on the football team's Twitter account.
An hour before the scheduled kick-off of Thursday's opening match at the Allianz Stadium, several hundred hooded fans in the Cologne colours invaded the Nice stands.
Clashes erupted, with some fans armed with chairs or iron bars torn from the stadium, and a total of 32 people were injured, including two police officers and a steward.
Four were hospitalised, with one -- a Parisian who had been among the German supporters -- in a critical condition after falling in the mayhem.
The club would "do everything in our power to clear up what happened and go with full consequence against those who chose violence," Wolf said.
"We owe that to our thousands of peaceful fans and football in general."
In comments on the club's website, sports director Christian Keller said he was "speechless".
"We wanted to celebrate a big, peaceful footballing fest," Keller said, adding that instead the events had only led to "suffering".
The violence prompted a delay of nearly an hour to the start of the game.
The Group D match eventually kicked off, ending in a 1-1 draw.
In August last year, a Ligue 1 game between Nice and Marseille was abandoned after a pitch invasion by fans, which was followed by a fight between supporters, players and staff of both teams.
In 2017, the kick-off of a Europa League game between Cologne and Arsenal was delayed by an hour after police made arrests at the Emirates Stadium as German fans occupied home sections of the ground.
